diff --git a/CHANGELOG.md b/CHANGELOG.md
index b5731b58f..014d5f2a0 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -37,6 +37,8 @@ Fixes to bugs found via fuzzing
 * Fixed improper parsing of numbers with too many decimal points.
 * Fixed exponential running time when raising a decimal number to a very large power (> 1 million) -- it now returns an overflow error.
 * Shared values that contain reference loops no longer cause a stack overflow when printing.
+* `sleep` no longer panics on `NaN`.
+* `switch` on ranges now work properly.
 
 Other bug fixes
 ---------------
@@ -47,7 +49,11 @@ Other bug fixes
 New features
 ------------
 
+* `#[derive(CustomType)]` is now available, driven by procedural macros in `rhai_codegen`.
+* A new `FuncRegistration` API is added to assist in registering native Rust functions into modules with various settings. Some of the original `Module::set_fn...` API is now deprecated.
 * Functions defined in plugin modules can now be marked as `volatile` which prevents it from being optimized away even under `OptimizationLevel::Full`.
+* Added `Engine::max_functions` and `Engine::set_max_functions` to limit the maximum number of functions allowed in a script. This s to guard against DOS attacks -- e.g. a simple closure `||` (two characters) is a function. When `max_function` is exceeded during script compilation, a new parse error, `TooManyFunctions`, is returned.
+* `Engine::get_interned_string` is made public instead of gated under `internals`.
 
 Enhancements
 ------------
@@ -57,6 +63,7 @@ Enhancements
 * `Token::FloatConstant` and `Token::DecimalConstant` now carry the original text representation for use in, say, a _token mapper_.
 * `Dynamic::is_fnptr` is made a public API.
 * `Scope::get_value_ref` and `Scope::get_value_mut` are added.
+* `TypeBuilder::with_name` now takes any `&str` instead of just `&'static str`.
 
 
 Version 1.16.3
diff --git a/Cargo.toml b/Cargo.toml
index e4f4da67a..615c78696 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -25,7 +25,7 @@ num-traits = { version = "0.2.0", default-features = false }
 once_cell = { version = "1.7.0", default-features = false, features = ["race"] }
 bitflags = { version = "2.0.0", default-features = false }
 smartstring = { version = "1.0.0", default-features = false }
-rhai_codegen = { version = "1.7.0", path = "codegen" }
+rhai_codegen = { version = "1.17.0", path = "codegen" }
 
 no-std-compat = { git = "https://gitlab.com/jD91mZM2/no-std-compat", version = "0.4.1", default-features = false, features = ["alloc"], optional = true }
 libm = { version = "0.2.0", default-features = false, optional = true }
@@ -165,3 +165,6 @@ features = ["document-features", "metadata", "serde", "internals", "decimal", "d
 # Notice that a custom modified version of `rustyline` is used which supports bracketed paste on Windows.
 # This can be moved to the official version when bracketed paste is added.
 rustyline = { git = "https://github.com/schungx/rustyline", branch = "v13" }
+
+# Patch SmartString to resolve an UB issue.
+smartstring = { git = "https://github.com/bodil/smartstring", ref = "refs/pull/34/head" }
diff --git a/codegen/Cargo.toml b/codegen/Cargo.toml
index 4c79d58ec..96b3d7ce8 100644
--- a/codegen/Cargo.toml
+++ b/codegen/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "rhai_codegen"
-version = "1.7.0"
+version = "1.17.0"
 edition = "2018"
 resolver = "2"
 authors = ["jhwgh1968", "Stephen Chung"]
diff --git a/codegen/src/custom_type.rs b/codegen/src/custom_type.rs
index 8b08af1fb..7982e5056 100644
--- a/codegen/src/custom_type.rs
+++ b/codegen/src/custom_type.rs
@@ -48,7 +48,7 @@ pub fn derive_custom_type_impl(input: DeriveInput) -> TokenStream {
 
     quote! {
         impl ::rhai::CustomType for #name {
-            fn build(mut builder: ::rhai::TypeBuilder<'_, Self>) {
+            fn build(mut builder: ::rhai::TypeBuilder<Self>) {
                 #accessors;
             }
         }
diff --git a/codegen/src/function.rs b/codegen/src/function.rs
index c377a8034..8f474d4cc 100644
--- a/codegen/src/function.rs
+++ b/codegen/src/function.rs
@@ -854,7 +854,7 @@ impl ExportedFn {
                 #[inline(always)] pub fn param_types() -> [TypeId; #arg_count] { [#(#input_type_exprs),*] }
             }
             #(#cfg_attrs)*
-            impl PluginFunction for #type_name {
+            impl PluginFunc for #type_name {
                 #[inline(always)]
                 fn call(&self, context: Option<NativeCallContext>, args: &mut [&mut Dynamic]) -> RhaiResult {
                     #(#unpack_statements)*
diff --git a/codegen/src/lib.rs b/codegen/src/lib.rs
index 09469d3b9..29088aaa1 100644
--- a/codegen/src/lib.rs
+++ b/codegen/src/lib.rs
@@ -345,19 +345,18 @@ pub fn set_exported_fn(args: proc_macro::TokenStream) -> proc_macro::TokenStream
         Ok((module_expr, export_name, rust_mod_path)) => {
             let gen_mod_path = crate::register::generated_module_path(&rust_mod_path);
 
-            #[cfg(feature = "metadata")]
-            let param_names = quote! {
-                Some(#gen_mod_path::Token::PARAM_NAMES)
+            let mut tokens = quote! {
+                let fx = FuncRegistration::new(#export_name).with_namespace(FnNamespace::Internal)
             };
-            #[cfg(not(feature = "metadata"))]
-            let param_names = quote! { None };
-
-            proc_macro::TokenStream::from(quote! {
-                #module_expr.set_fn(#export_name, FnNamespace::Internal, FnAccess::Public,
-                                    #param_names,
-                                    &#gen_mod_path::Token::param_types(),
-                                    #gen_mod_path::Token().into())
-            })
+            #[cfg(feature = "metadata")]
+            tokens.extend(quote! {
+                .with_params_info(#gen_mod_path::Token::PARAM_NAMES)
+            });
+            tokens.extend(quote! {
+                ;
+                #module_expr.set_fn_raw_with_options(fx, &#gen_mod_path::Token::param_types(), #gen_mod_path::Token().into());
+            });
+            tokens.into()
         }
         Err(e) => e.to_compile_error().into(),
     }
@@ -394,19 +393,18 @@ pub fn set_exported_global_fn(args: proc_macro::TokenStream) -> proc_macro::Toke
         Ok((module_expr, export_name, rust_mod_path)) => {
             let gen_mod_path = crate::register::generated_module_path(&rust_mod_path);
 
-            #[cfg(feature = "metadata")]
-            let param_names = quote! {
-                Some(#gen_mod_path::Token::PARAM_NAMES)
+            let mut tokens = quote! {
+                let fx = FuncRegistration::new(#export_name).with_namespace(FnNamespace::Global)
             };
-            #[cfg(not(feature = "metadata"))]
-            let param_names = quote! { None };
-
-            proc_macro::TokenStream::from(quote! {
-                #module_expr.set_fn(#export_name, FnNamespace::Global, FnAccess::Public,
-                                    #param_names,
-                                    &#gen_mod_path::Token::param_types(),
-                                    #gen_mod_path::Token().into())
-            })
+            #[cfg(feature = "metadata")]
+            tokens.extend(quote! {
+                .with_params_info(#gen_mod_path::Token::PARAM_NAMES)
+            });
+            tokens.extend(quote! {
+                ;
+                #module_expr.set_fn_raw_with_options(fx, &#gen_mod_path::Token::param_types(), #gen_mod_path::Token().into());
+            });
+            tokens.into()
         }
         Err(e) => e.to_compile_error().into(),
     }
diff --git a/codegen/src/rhai_module.rs b/codegen/src/rhai_module.rs
index b04d88a81..903b82ff7 100644
--- a/codegen/src/rhai_module.rs
+++ b/codegen/src/rhai_module.rs
@@ -5,8 +5,8 @@ use std::collections::BTreeMap;
 
 use crate::attrs::ExportScope;
 use crate::function::{
-    flatten_type_groups, print_type, ExportedFn, FnNamespaceAccess, FnSpecialAccess, FN_GET,
-    FN_IDX_GET, FN_IDX_SET, FN_SET,
+    print_type, ExportedFn, FnNamespaceAccess, FnSpecialAccess, FN_GET, FN_IDX_GET, FN_IDX_SET,
+    FN_SET,
 };
 use crate::module::Module;
 
@@ -39,8 +39,6 @@ pub fn generate_body(
     let mut set_const_statements = Vec::new();
     let mut add_mod_blocks = Vec::new();
     let mut set_flattened_mod_blocks = Vec::new();
-    let str_type_path = syn::parse2::<syn::Path>(quote! { str }).unwrap();
-    let string_type_path = syn::parse2::<syn::Path>(quote! { String }).unwrap();
 
     for ExportedConst {
         name: const_name,
@@ -146,49 +144,6 @@ pub fn generate_body(
         );
         let reg_names = function.exported_names();
 
-        let fn_input_types: Vec<_> = function
-            .arg_list()
-            .map(|fn_arg| match fn_arg {
-                syn::FnArg::Receiver(..) => unreachable!("receiver fn outside impl!?"),
-                syn::FnArg::Typed(syn::PatType { ref ty, .. }) => {
-                    let arg_type = match flatten_type_groups(ty.as_ref()) {
-                        syn::Type::Reference(syn::TypeReference {
-                            mutability: None,
-                            ref elem,
-                            ..
-                        }) => match flatten_type_groups(elem.as_ref()) {
-                            syn::Type::Path(ref p) if p.path == str_type_path => {
-                                syn::parse2::<syn::Type>(quote! {
-                                ImmutableString })
-                                .unwrap()
-                            }
-                            _ => unreachable!("non-string shared reference!?"),
-                        },
-                        syn::Type::Path(ref p) if p.path == string_type_path => {
-                            syn::parse2::<syn::Type>(quote! {
-                            ImmutableString })
-                            .unwrap()
-                        }
-                        syn::Type::Reference(syn::TypeReference {
-                            mutability: Some(_),
-                            ref elem,
-                            ..
-                        }) => match flatten_type_groups(elem.as_ref()) {
-                            syn::Type::Path(ref p) => syn::parse2::<syn::Type>(quote! {
-                            #p })
-                            .unwrap(),
-                            _ => unreachable!("invalid mutable reference!?"),
-                        },
-                        t => t.clone(),
-                    };
-
-                    syn::parse2::<syn::Expr>(quote! {
-                    TypeId::of::<#arg_type>()})
-                    .unwrap()
-                }
-            })
-            .collect();
-
         let cfg_attrs: Vec<_> = function
             .cfg_attrs()
             .iter()
@@ -226,33 +181,34 @@ pub fn generate_body(
                 fn_literal.span(),
             );
 
+            let mut tokens = quote! {
+                #(#cfg_attrs)*
+                FuncRegistration::new(#fn_literal).with_namespace(FnNamespace::#ns_str)
+            };
             #[cfg(feature = "metadata")]
-            let (param_names, comments) = (
-                quote! { Some(#fn_token_name::PARAM_NAMES) },
-                function
+            {
+                tokens.extend(quote! {
+                    .with_params_info(#fn_token_name::PARAM_NAMES)
+                });
+
+                let comments = function
                     .comments()
                     .iter()
                     .map(|s| syn::LitStr::new(s, Span::call_site()))
-                    .collect::<Vec<_>>(),
-            );
-            #[cfg(not(feature = "metadata"))]
-            let (param_names, comments) = (quote! { None }, Vec::<syn::LitStr>::new());
+                    .collect::<Vec<_>>();
 
-            set_fn_statements.push(if comments.is_empty() {
-                syn::parse2::<syn::Stmt>(quote! {
-                    #(#cfg_attrs)*
-                    m.set_fn(#fn_literal, FnNamespace::#ns_str, FnAccess::Public,
-                             #param_names, &[#(#fn_input_types),*], #fn_token_name().into());
-                })
-                .unwrap()
-            } else {
-                syn::parse2::<syn::Stmt>(quote! {
-                    #(#cfg_attrs)*
-                    m.set_fn_with_comments(#fn_literal, FnNamespace::#ns_str, FnAccess::Public,
-                             #param_names, &[#(#fn_input_types),*], &[#(#comments),*], #fn_token_name().into());
-                })
-                .unwrap()
+                if !comments.is_empty() {
+                    tokens.extend(quote! {
+                        .with_comments(&[#(#comments),*])
+                    });
+                }
+            }
+
+            tokens.extend(quote! {
+                .set_into_module_raw(m, &#fn_token_name::param_types(), #fn_token_name().into());
             });
+
+            set_fn_statements.push(syn::parse2::<syn::Stmt>(tokens).unwrap());
         }
 
         gen_fn_tokens.push(quote! {
diff --git a/codegen/src/test/function.rs b/codegen/src/test/function.rs
index f07a4cb20..c3e1b47e7 100644
--- a/codegen/src/test/function.rs
+++ b/codegen/src/test/function.rs
@@ -279,7 +279,7 @@ mod generate_tests {
                     pub const PARAM_NAMES: &'static [&'static str] = &["()"];
                     #[inline(always)] pub fn param_types() -> [TypeId; 0usize] { [] }
                 }
-                impl PluginFunction for Token {
+                impl PluginFunc for Token {
                     #[inline(always)] fn call(&self, context: Option<NativeCallContext>, args: &mut [&mut Dynamic]) -> RhaiResult {
                         Ok(Dynamic::from(do_nothing()))
                     }
@@ -318,7 +318,7 @@ mod generate_tests {
                     pub const PARAM_NAMES: &'static [&'static str] = &["x: usize", "()"];
                     #[inline(always)] pub fn param_types() -> [TypeId; 1usize] { [TypeId::of::<usize>()] }
                 }
-                impl PluginFunction for Token {
+                impl PluginFunc for Token {
                     #[inline(always)]
                     fn call(&self, context: Option<NativeCallContext>, args: &mut [&mut Dynamic]) -> RhaiResult {
                         let arg0 = mem::take(args[0usize]).cast::<usize>();
@@ -359,7 +359,7 @@ mod generate_tests {
                     pub const PARAM_NAMES: &'static [&'static str] = &["x: usize", "()"];
                     #[inline(always)] pub fn param_types() -> [TypeId; 1usize] { [TypeId::of::<usize>()] }
                 }
-                impl PluginFunction for Token {
+                impl PluginFunc for Token {
                     #[inline(always)]
                     fn call(&self, context: Option<NativeCallContext>, args: &mut [&mut Dynamic]) -> RhaiResult {
                         let arg0 = mem::take(args[0usize]).cast::<usize>();
@@ -403,7 +403,7 @@ mod generate_tests {
                     pub const PARAM_NAMES: &'static [&'static str] = &["rhai::Dynamic"];
                     #[inline(always)] pub fn param_types() -> [TypeId; 0usize] { [] }
                 }
-                impl PluginFunction for Token {
+                impl PluginFunc for Token {
                     #[inline(always)]
                     fn call(&self, context: Option<NativeCallContext>, args: &mut [&mut Dynamic]) -> RhaiResult {
                         Ok(Dynamic::from(return_dynamic()))
@@ -438,7 +438,7 @@ mod generate_tests {
                 pub const PARAM_NAMES: &'static [&'static str] = &["x: usize", "()"];
                 #[inline(always)] pub fn param_types() -> [TypeId; 1usize] { [TypeId::of::<usize>()] }
             }
-            impl PluginFunction for TestStruct {
+            impl PluginFunc for TestStruct {
                 #[inline(always)]
                 fn call(&self, context: Option<NativeCallContext>, args: &mut [&mut Dynamic]) -> RhaiResult {
                     let arg0 = mem::take(args[0usize]).cast::<usize>();
@@ -473,7 +473,7 @@ mod generate_tests {
                     pub const PARAM_NAMES: &'static [&'static str] = &["x: usize", "y: usize", "usize"];
                     #[inline(always)] pub fn param_types() -> [TypeId; 2usize] { [TypeId::of::<usize>(), TypeId::of::<usize>()] }
                 }
-                impl PluginFunction for Token {
+                impl PluginFunc for Token {
                     #[inline(always)]
                     fn call(&self, context: Option<NativeCallContext>, args: &mut [&mut Dynamic]) -> RhaiResult {
                         let arg0 = mem::take(args[0usize]).cast::<usize>();
@@ -515,7 +515,7 @@ mod generate_tests {
                     pub const PARAM_NAMES: &'static [&'static str] = &["x: &mut usize", "y: usize", "()"];
                     #[inline(always)] pub fn param_types() -> [TypeId; 2usize] { [TypeId::of::<usize>(), TypeId::of::<usize>()] }
                 }
-                impl PluginFunction for Token {
+                impl PluginFunc for Token {
                     #[inline(always)]
                     fn call(&self, context: Option<NativeCallContext>, args: &mut [&mut Dynamic]) -> RhaiResult {
                         let arg1 = mem::take(args[1usize]).cast::<usize>();
@@ -558,7 +558,7 @@ mod generate_tests {
                     pub const PARAM_NAMES: &'static [&'static str] = &["message: &str", "()"];
                     #[inline(always)] pub fn param_types() -> [TypeId; 1usize] { [TypeId::of::<ImmutableString>()] }
                 }
-                impl PluginFunction for Token {
+                impl PluginFunc for Token {
                     #[inline(always)]
                     fn call(&self, context: Option<NativeCallContext>, args: &mut [&mut Dynamic]) -> RhaiResult {
                         let arg0 = mem::take(args[0usize]).into_immutable_string().unwrap();
diff --git a/codegen/src/test/module.rs b/codegen/src/test/module.rs
index 4a0ce94b1..a2764734b 100644
--- a/codegen/src/test/module.rs
+++ b/codegen/src/test/module.rs
@@ -378,9 +378,8 @@ mod generate_tests {
                 #[allow(unused_mut)]
                 #[doc(hidden)]
                 pub fn rhai_generate_into_module(m: &mut Module, flatten: bool) {
-                    m.set_fn("get_mystic_number", FnNamespace::Internal, FnAccess::Public,
-                             Some(get_mystic_number_token::PARAM_NAMES), &[],
-                             get_mystic_number_token().into());
+                    FuncRegistration::new("get_mystic_number").with_namespace(FnNamespace::Internal).with_params_info(get_mystic_number_token::PARAM_NAMES)
+                        .set_into_module_raw(m, &get_mystic_number_token::param_types(), get_mystic_number_token().into());
                     if flatten {} else {}
                 }
                 #[allow(non_camel_case_types)]
@@ -391,7 +390,7 @@ mod generate_tests {
                     pub const PARAM_NAMES: &'static [&'static str] = &["INT"];
                     #[inline(always)] pub fn param_types() -> [TypeId; 0usize] { [] }
                 }
-                impl PluginFunction for get_mystic_number_token {
+                impl PluginFunc for get_mystic_number_token {
                     #[inline(always)]
                     fn call(&self, context: Option<NativeCallContext>, args: &mut [&mut Dynamic]) -> RhaiResult {
                         Ok(Dynamic::from(get_mystic_number()))
@@ -473,11 +472,12 @@ mod generate_tests {
                 #[allow(unused_mut)]
                 #[doc(hidden)]
                 pub fn rhai_generate_into_module(m: &mut Module, flatten: bool) {
-                    m.set_fn_with_comments("get_mystic_number", FnNamespace::Internal, FnAccess::Public,
-                             Some(get_mystic_number_token::PARAM_NAMES), &[], &[
-                                 "/// This is a doc-comment.\n/// Another line.\n/// block doc-comment \n/// Final line.",
-                                 "/** doc-comment\n                    in multiple lines\n                 */"
-                             ], get_mystic_number_token().into());
+                    FuncRegistration::new("get_mystic_number").with_namespace(FnNamespace::Internal).with_params_info(get_mystic_number_token::PARAM_NAMES)
+                        .with_comments(&[
+                            "/// This is a doc-comment.\n/// Another line.\n/// block doc-comment \n/// Final line.",
+                            "/** doc-comment\n                    in multiple lines\n                 */"
+                        ])
+                        .set_into_module_raw(m, &get_mystic_number_token::param_types(), get_mystic_number_token().into());
                     m.set_custom_type_with_comments::<String>("World", &["/// We are the world!"]);
                     if flatten {} else {}
                 }
@@ -489,7 +489,7 @@ mod generate_tests {
                     pub const PARAM_NAMES: &'static [&'static str] = &["INT"];
                     #[inline(always)] pub fn param_types() -> [TypeId; 0usize] { [] }
                 }
-                impl PluginFunction for get_mystic_number_token {
+                impl PluginFunc for get_mystic_number_token {
                     #[inline(always)]
                     fn call(&self, context: Option<NativeCallContext>, args: &mut [&mut Dynamic]) -> RhaiResult {
                         Ok(Dynamic::from(get_mystic_number()))
@@ -537,9 +537,8 @@ mod generate_tests {
                 #[allow(unused_mut)]
                 #[doc(hidden)]
                 pub fn rhai_generate_into_module(m: &mut Module, flatten: bool) {
-                    m.set_fn("add_one_to", FnNamespace::Global, FnAccess::Public,
-                             Some(add_one_to_token::PARAM_NAMES), &[TypeId::of::<INT>()],
-                             add_one_to_token().into());
+                    FuncRegistration::new("add_one_to").with_namespace(FnNamespace::Global).with_params_info(add_one_to_token::PARAM_NAMES)
+                        .set_into_module_raw(m, &add_one_to_token::param_types(), add_one_to_token().into());
                     if flatten {} else {}
                 }
                 #[allow(non_camel_case_types)]
@@ -550,7 +549,7 @@ mod generate_tests {
                     pub const PARAM_NAMES: &'static [&'static str] = &["x: INT", "INT"];
                     #[inline(always)] pub fn param_types() -> [TypeId; 1usize] { [TypeId::of::<INT>()] }
                 }
-                impl PluginFunction for add_one_to_token {
+                impl PluginFunc for add_one_to_token {
                     #[inline(always)]
                     fn call(&self, context: Option<NativeCallContext>, args: &mut [&mut Dynamic]) -> RhaiResult {
                         let arg0 = mem::take(args[0usize]).cast::<INT>();
@@ -598,9 +597,8 @@ mod generate_tests {
                 #[allow(unused_mut)]
                 #[doc(hidden)]
                 pub fn rhai_generate_into_module(m: &mut Module, flatten: bool) {
-                    m.set_fn("add_one_to", FnNamespace::Internal, FnAccess::Public, Some(add_one_to_token::PARAM_NAMES),
-                             &[TypeId::of::<INT>()],
-                             add_one_to_token().into());
+                    FuncRegistration::new("add_one_to").with_namespace(FnNamespace::Internal).with_params_info(add_one_to_token::PARAM_NAMES)
+                        .set_into_module_raw(m, &add_one_to_token::param_types(), add_one_to_token().into());
                     if flatten {} else {}
                 }
                 #[allow(non_camel_case_types)]
@@ -611,7 +609,7 @@ mod generate_tests {
                     pub const PARAM_NAMES: &'static [&'static str] = &["x: INT", "INT"];
                     #[inline(always)] pub fn param_types() -> [TypeId; 1usize] { [TypeId::of::<INT>()] }
                 }
-                impl PluginFunction for add_one_to_token {
+                impl PluginFunc for add_one_to_token {
                     #[inline(always)]
                     fn call(&self, context: Option<NativeCallContext>, args: &mut [&mut Dynamic]) -> RhaiResult {
                         let arg0 = mem::take(args[0usize]).cast::<INT>();
@@ -670,12 +668,10 @@ mod generate_tests {
                 #[allow(unused_mut)]
                 #[doc(hidden)]
                 pub fn rhai_generate_into_module(m: &mut Module, flatten: bool) {
-                    m.set_fn("add_n", FnNamespace::Internal, FnAccess::Public, Some(add_one_to_token::PARAM_NAMES),
-                             &[TypeId::of::<INT>()],
-                             add_one_to_token().into());
-                    m.set_fn("add_n", FnNamespace::Internal, FnAccess::Public, Some(add_n_to_token::PARAM_NAMES),
-                             &[TypeId::of::<INT>(), TypeId::of::<INT>()],
-                             add_n_to_token().into());
+                    FuncRegistration::new("add_n").with_namespace(FnNamespace::Internal).with_params_info(add_one_to_token::PARAM_NAMES)
+                        .set_into_module_raw(m, &add_one_to_token::param_types(), add_one_to_token().into());
+                    FuncRegistration::new("add_n").with_namespace(FnNamespace::Internal).with_params_info(add_n_to_token::PARAM_NAMES)
+                        .set_into_module_raw(m, &add_n_to_token::param_types(), add_n_to_token().into());
                     if flatten {} else {}
                 }
                 #[allow(non_camel_case_types)]
@@ -686,7 +682,7 @@ mod generate_tests {
                     pub const PARAM_NAMES: &'static [&'static str] = &["x: INT", "INT"];
                     #[inline(always)] pub fn param_types() -> [TypeId; 1usize] { [TypeId::of::<INT>()] }
                 }
-                impl PluginFunction for add_one_to_token {
+                impl PluginFunc for add_one_to_token {
                     #[inline(always)]
                     fn call(&self, context: Option<NativeCallContext>, args: &mut [&mut Dynamic]) -> RhaiResult {
                         let arg0 = mem::take(args[0usize]).cast::<INT>();
@@ -707,7 +703,7 @@ mod generate_tests {
                     pub const PARAM_NAMES: &'static [&'static str] = &["x: INT", "y: INT", "INT"];
                     #[inline(always)] pub fn param_types() -> [TypeId; 2usize] { [TypeId::of::<INT>(), TypeId::of::<INT>()] }
                 }
-                impl PluginFunction for add_n_to_token {
+                impl PluginFunc for add_n_to_token {
                     #[inline(always)]
                     fn call(&self, context: Option<NativeCallContext>, args: &mut [&mut Dynamic]) -> RhaiResult {
                         let arg0 = mem::take(args[0usize]).cast::<INT>();
@@ -756,9 +752,8 @@ mod generate_tests {
                 #[allow(unused_mut)]
                 #[doc(hidden)]
                 pub fn rhai_generate_into_module(m: &mut Module, flatten: bool) {
-                    m.set_fn("add_together", FnNamespace::Internal, FnAccess::Public, Some(add_together_token::PARAM_NAMES),
-                             &[TypeId::of::<INT>(), TypeId::of::<INT>()],
-                             add_together_token().into());
+                    FuncRegistration::new("add_together").with_namespace(FnNamespace::Internal).with_params_info(add_together_token::PARAM_NAMES)
+                        .set_into_module_raw(m, &add_together_token::param_types(), add_together_token().into());
                     if flatten {} else {}
                 }
                 #[allow(non_camel_case_types)]
@@ -769,7 +764,7 @@ mod generate_tests {
                     pub const PARAM_NAMES: &'static [&'static str] = &["x: INT", "y: INT", "INT"];
                     #[inline(always)] pub fn param_types() -> [TypeId; 2usize] { [TypeId::of::<INT>(), TypeId::of::<INT>()] }
                 }
-                impl PluginFunction for add_together_token {
+                impl PluginFunc for add_together_token {
                     #[inline(always)]
                     fn call(&self, context: Option<NativeCallContext>, args: &mut [&mut Dynamic]) -> RhaiResult {
                         let arg0 = mem::take(args[0usize]).cast::<INT>();
@@ -819,15 +814,12 @@ mod generate_tests {
                 #[allow(unused_mut)]
                 #[doc(hidden)]
                 pub fn rhai_generate_into_module(m: &mut Module, flatten: bool) {
-                    m.set_fn("add", FnNamespace::Internal, FnAccess::Public, Some(add_together_token::PARAM_NAMES),
-                             &[TypeId::of::<INT>(), TypeId::of::<INT>()],
-                             add_together_token().into());
-                    m.set_fn("+", FnNamespace::Internal, FnAccess::Public, Some(add_together_token::PARAM_NAMES),
-                             &[TypeId::of::<INT>(), TypeId::of::<INT>()],
-                             add_together_token().into());
-                    m.set_fn("add_together", FnNamespace::Internal, FnAccess::Public, Some(add_together_token::PARAM_NAMES),
-                             &[TypeId::of::<INT>(), TypeId::of::<INT>()],
-                             add_together_token().into());
+                    FuncRegistration::new("add").with_namespace(FnNamespace::Internal).with_params_info(add_together_token::PARAM_NAMES)
+                        .set_into_module_raw(m, &add_together_token::param_types(), add_together_token().into());
+                    FuncRegistration::new("+").with_namespace(FnNamespace::Internal).with_params_info(add_together_token::PARAM_NAMES)
+                        .set_into_module_raw(m, &add_together_token::param_types(), add_together_token().into());
+                    FuncRegistration::new("add_together").with_namespace(FnNamespace::Internal).with_params_info(add_together_token::PARAM_NAMES)
+                        .set_into_module_raw(m, &add_together_token::param_types(), add_together_token().into());
                     if flatten {} else {}
                 }
                 #[allow(non_camel_case_types)]
@@ -838,7 +830,7 @@ mod generate_tests {
                     pub const PARAM_NAMES: &'static [&'static str] = &["x: INT", "y: INT", "INT"];
                     #[inline(always)] pub fn param_types() -> [TypeId; 2usize] { [TypeId::of::<INT>(), TypeId::of::<INT>()] }
                 }
-                impl PluginFunction for add_together_token {
+                impl PluginFunc for add_together_token {
                     #[inline(always)]
                     fn call(&self, context: Option<NativeCallContext>, args: &mut [&mut Dynamic]) -> RhaiResult {
                         let arg0 = mem::take(args[0usize]).cast::<INT>();
@@ -901,9 +893,8 @@ mod generate_tests {
                 #[allow(unused_mut)]
                 #[doc(hidden)]
                 pub fn rhai_generate_into_module(m: &mut Module, flatten: bool) {
-                    m.set_fn("get_mystic_number", FnNamespace::Internal, FnAccess::Public,
-                             Some(get_mystic_number_token::PARAM_NAMES), &[TypeId::of::<Hello>()],
-                             get_mystic_number_token().into());
+                    FuncRegistration::new("get_mystic_number").with_namespace(FnNamespace::Internal).with_params_info(get_mystic_number_token::PARAM_NAMES)
+                        .set_into_module_raw(m, &get_mystic_number_token::param_types(), get_mystic_number_token().into());
                     m.set_var("MYSTIC_NUMBER", MYSTIC_NUMBER);
                     m.set_custom_type::<Foo>("Hello");
                     if flatten {} else {}
@@ -917,7 +908,7 @@ mod generate_tests {
                     pub const PARAM_NAMES: &'static [&'static str] = &["x: &mut Hello", "INT"];
                     #[inline(always)] pub fn param_types() -> [TypeId; 1usize] { [TypeId::of::<Hello>()] }
                 }
-                impl PluginFunction for get_mystic_number_token {
+                impl PluginFunc for get_mystic_number_token {
                     #[inline(always)]
                     fn call(&self, context: Option<NativeCallContext>, args: &mut [&mut Dynamic]) -> RhaiResult {
                         let arg0 = &mut args[0usize].write_lock::<Hello>().unwrap();
@@ -1121,9 +1112,8 @@ mod generate_tests {
                 #[allow(unused_mut)]
                 #[doc(hidden)]
                 pub fn rhai_generate_into_module(m: &mut Module, flatten: bool) {
-                    m.set_fn("get_mystic_number", FnNamespace::Internal, FnAccess::Public,
-                             Some(get_mystic_number_token::PARAM_NAMES), &[],
-                             get_mystic_number_token().into());
+                    FuncRegistration::new("get_mystic_number").with_namespace(FnNamespace::Internal).with_params_info(get_mystic_number_token::PARAM_NAMES)
+                        .set_into_module_raw(m, &get_mystic_number_token::param_types(), get_mystic_number_token().into());
                     if flatten {} else {}
                 }
                 #[allow(non_camel_case_types)]
@@ -1134,7 +1124,7 @@ mod generate_tests {
                     pub const PARAM_NAMES: &'static [&'static str] = &["INT"];
                     #[inline(always)] pub fn param_types() -> [TypeId; 0usize] { [] }
                 }
-                impl PluginFunction for get_mystic_number_token {
+                impl PluginFunc for get_mystic_number_token {
                     #[inline(always)]
                     fn call(&self, context: Option<NativeCallContext>, args: &mut [&mut Dynamic]) -> RhaiResult {
                         Ok(Dynamic::from(get_mystic_number()))
@@ -1215,9 +1205,8 @@ mod generate_tests {
                 #[allow(unused_mut)]
                 #[doc(hidden)]
                 pub fn rhai_generate_into_module(m: &mut Module, flatten: bool) {
-                    m.set_fn("print_out_to", FnNamespace::Internal, FnAccess::Public, Some(print_out_to_token::PARAM_NAMES),
-                             &[TypeId::of::<ImmutableString>()],
-                             print_out_to_token().into());
+                    FuncRegistration::new("print_out_to").with_namespace(FnNamespace::Internal).with_params_info(print_out_to_token::PARAM_NAMES)
+                         .set_into_module_raw(m, &print_out_to_token::param_types(), print_out_to_token().into());
                     if flatten {} else {}
                 }
                 #[allow(non_camel_case_types)]
@@ -1228,7 +1217,7 @@ mod generate_tests {
                     pub const PARAM_NAMES: &'static [&'static str] = &["x: &str", "()"];
                     #[inline(always)] pub fn param_types() -> [TypeId; 1usize] { [TypeId::of::<ImmutableString>()] }
                 }
-                impl PluginFunction for print_out_to_token {
+                impl PluginFunc for print_out_to_token {
                     #[inline(always)]
                     fn call(&self, context: Option<NativeCallContext>, args: &mut [&mut Dynamic]) -> RhaiResult {
                         let arg0 = mem::take(args[0usize]).into_immutable_string().unwrap();
@@ -1276,9 +1265,8 @@ mod generate_tests {
                 #[allow(unused_mut)]
                 #[doc(hidden)]
                 pub fn rhai_generate_into_module(m: &mut Module, flatten: bool) {
-                    m.set_fn("print_out_to", FnNamespace::Internal, FnAccess::Public, Some(print_out_to_token::PARAM_NAMES),
-                             &[TypeId::of::<ImmutableString>()],
-                             print_out_to_token().into());
+                    FuncRegistration::new("print_out_to").with_namespace(FnNamespace::Internal).with_params_info(print_out_to_token::PARAM_NAMES)
+                         .set_into_module_raw(m, &print_out_to_token::param_types(), print_out_to_token().into());
                     if flatten {} else {}
                 }
                 #[allow(non_camel_case_types)]
@@ -1289,7 +1277,7 @@ mod generate_tests {
                     pub const PARAM_NAMES: &'static [&'static str] = &["x: String", "()"];
                     #[inline(always)] pub fn param_types() -> [TypeId; 1usize] { [TypeId::of::<ImmutableString>()] }
                 }
-                impl PluginFunction for print_out_to_token {
+                impl PluginFunc for print_out_to_token {
                     #[inline(always)]
                     fn call(&self, context: Option<NativeCallContext>, args: &mut [&mut Dynamic]) -> RhaiResult {
                         let arg0 = mem::take(args[0usize]).into_string().unwrap();
@@ -1338,9 +1326,8 @@ mod generate_tests {
                 #[allow(unused_mut)]
                 #[doc(hidden)]
                 pub fn rhai_generate_into_module(m: &mut Module, flatten: bool) {
-                    m.set_fn("foo", FnNamespace::Internal, FnAccess::Public, Some(foo_token::PARAM_NAMES),
-                             &[TypeId::of::<FLOAT>(), TypeId::of::<INT>()],
-                             foo_token().into());
+                    FuncRegistration::new("foo").with_namespace(FnNamespace::Internal).with_params_info(foo_token::PARAM_NAMES)
+                         .set_into_module_raw(m, &foo_token::param_types(), foo_token().into());
                     if flatten {} else {}
                 }
                 #[allow(non_camel_case_types)]
@@ -1351,7 +1338,7 @@ mod generate_tests {
                     pub const PARAM_NAMES: &'static [&'static str] = &["x: &mut FLOAT", "y: INT", "FLOAT"];
                     #[inline(always)] pub fn param_types() -> [TypeId; 2usize] { [TypeId::of::<FLOAT>(), TypeId::of::<INT>()] }
                 }
-                impl PluginFunction for foo_token {
+                impl PluginFunc for foo_token {
                     #[inline(always)]
                     fn call(&self, context: Option<NativeCallContext>, args: &mut [&mut Dynamic]) -> RhaiResult {
                         let arg1 = mem::take(args[1usize]).cast::<INT>();
@@ -1400,9 +1387,8 @@ mod generate_tests {
                 #[allow(unused_mut)]
                 #[doc(hidden)]
                 pub fn rhai_generate_into_module(m: &mut Module, flatten: bool) {
-                    m.set_fn("increment", FnNamespace::Internal, FnAccess::Public, Some(increment_token::PARAM_NAMES),
-                             &[TypeId::of::<FLOAT>()],
-                             increment_token().into());
+                    FuncRegistration::new("increment").with_namespace(FnNamespace::Internal).with_params_info(increment_token::PARAM_NAMES)
+                         .set_into_module_raw(m, &increment_token::param_types(), increment_token().into());
                     if flatten {} else {}
                 }
                 #[allow(non_camel_case_types)]
@@ -1413,7 +1399,7 @@ mod generate_tests {
                     pub const PARAM_NAMES: &'static [&'static str] = &["x: &mut FLOAT", "()"];
                     #[inline(always)] pub fn param_types() -> [TypeId; 1usize] { [TypeId::of::<FLOAT>()] }
                 }
-                impl PluginFunction for increment_token {
+                impl PluginFunc for increment_token {
                     #[inline(always)]
                     fn call(&self, context: Option<NativeCallContext>, args: &mut [&mut Dynamic]) -> RhaiResult {
                         let arg0 = &mut args[0usize].write_lock::<FLOAT>().unwrap();
@@ -1465,9 +1451,8 @@ mod generate_tests {
                     #[allow(unused_mut)]
                     #[doc(hidden)]
                     pub fn rhai_generate_into_module(m: &mut Module, flatten: bool) {
-                        m.set_fn("increment", FnNamespace::Internal, FnAccess::Public, Some(increment_token::PARAM_NAMES),
-                                 &[TypeId::of::<FLOAT>()],
-                                 increment_token().into());
+                    FuncRegistration::new("increment").with_namespace(FnNamespace::Internal).with_params_info(increment_token::PARAM_NAMES)
+                             .set_into_module_raw(m, &increment_token::param_types(), increment_token().into());
                         if flatten {} else {}
                     }
                     #[allow(non_camel_case_types)]
@@ -1478,7 +1463,7 @@ mod generate_tests {
                         pub const PARAM_NAMES: &'static [&'static str] = &["x: &mut FLOAT", "()"];
                         #[inline(always)] pub fn param_types() -> [TypeId; 1usize] { [TypeId::of::<FLOAT>()] }
                     }
-                    impl PluginFunction for increment_token {
+                    impl PluginFunc for increment_token {
                         #[inline(always)]
                         fn call(&self, context: Option<NativeCallContext>, args: &mut [&mut Dynamic]) -> RhaiResult {
                             let arg0 = &mut args[0usize].write_lock::<FLOAT>().unwrap();
@@ -1552,9 +1537,8 @@ mod generate_tests {
                     #[allow(unused_mut)]
                     #[doc(hidden)]
                     pub fn rhai_generate_into_module(m: &mut Module, flatten: bool) {
-                        m.set_fn("increment", FnNamespace::Internal, FnAccess::Public, Some(increment_token::PARAM_NAMES),
-                                 &[TypeId::of::<FLOAT>()],
-                                 increment_token().into());
+                    FuncRegistration::new("increment").with_namespace(FnNamespace::Internal).with_params_info(increment_token::PARAM_NAMES)
+                             .set_into_module_raw(m, &increment_token::param_types(), increment_token().into());
                         if flatten {} else {}
                     }
                     #[allow(non_camel_case_types)]
@@ -1565,7 +1549,7 @@ mod generate_tests {
                         pub const PARAM_NAMES: &'static [&'static str] = &["x: &mut FLOAT", "()"];
                         #[inline(always)] pub fn param_types() -> [TypeId; 1usize] { [TypeId::of::<FLOAT>()] }
                     }
-                    impl PluginFunction for increment_token {
+                    impl PluginFunc for increment_token {
                         #[inline(always)]
                         fn call(&self, context: Option<NativeCallContext>, args: &mut [&mut Dynamic]) -> RhaiResult {
                             let arg0 = &mut args[0usize].write_lock::<FLOAT>().unwrap();
@@ -1640,9 +1624,8 @@ mod generate_tests {
                 #[allow(unused_mut)]
                 #[doc(hidden)]
                 pub fn rhai_generate_into_module(m: &mut Module, flatten: bool) {
-                    m.set_fn("get$square", FnNamespace::Global, FnAccess::Public, Some(int_foo_token::PARAM_NAMES),
-                             &[TypeId::of::<u64>()],
-                             int_foo_token().into());
+                    FuncRegistration::new("get$square").with_namespace(FnNamespace::Global).with_params_info(int_foo_token::PARAM_NAMES)
+                         .set_into_module_raw(m, &int_foo_token::param_types(), int_foo_token().into());
                     if flatten {} else {}
                 }
                 #[allow(non_camel_case_types)]
@@ -1653,7 +1636,7 @@ mod generate_tests {
                     pub const PARAM_NAMES: &'static [&'static str] = &["x: &mut u64", "u64"];
                     #[inline(always)] pub fn param_types() -> [TypeId; 1usize] { [TypeId::of::<u64>()] }
                 }
-                impl PluginFunction for int_foo_token {
+                impl PluginFunc for int_foo_token {
                     #[inline(always)]
                     fn call(&self, context: Option<NativeCallContext>, args: &mut [&mut Dynamic]) -> RhaiResult {
                         let arg0 = &mut args[0usize].write_lock::<u64>().unwrap();
@@ -1702,12 +1685,10 @@ mod generate_tests {
                 #[allow(unused_mut)]
                 #[doc(hidden)]
                 pub fn rhai_generate_into_module(m: &mut Module, flatten: bool) {
-                    m.set_fn("square", FnNamespace::Internal, FnAccess::Public, Some(int_foo_token::PARAM_NAMES),
-                             &[TypeId::of::<u64>()],
-                             int_foo_token().into());
-                    m.set_fn("get$square", FnNamespace::Global, FnAccess::Public, Some(int_foo_token::PARAM_NAMES),
-                             &[TypeId::of::<u64>()],
-                             int_foo_token().into());
+                    FuncRegistration::new("square").with_namespace(FnNamespace::Internal).with_params_info(int_foo_token::PARAM_NAMES)
+                         .set_into_module_raw(m, &int_foo_token::param_types(), int_foo_token().into());
+                    FuncRegistration::new("get$square").with_namespace(FnNamespace::Global).with_params_info(int_foo_token::PARAM_NAMES)
+                         .set_into_module_raw(m, &int_foo_token::param_types(), int_foo_token().into());
                     if flatten {} else {}
                 }
                 #[allow(non_camel_case_types)]
@@ -1718,7 +1699,7 @@ mod generate_tests {
                     pub const PARAM_NAMES: &'static [&'static str] = &["x: &mut u64", "u64"];
                     #[inline(always)] pub fn param_types() -> [TypeId; 1usize] { [TypeId::of::<u64>()] }
                 }
-                impl PluginFunction for int_foo_token {
+                impl PluginFunc for int_foo_token {
                     #[inline(always)]
                     fn call(&self, context: Option<NativeCallContext>, args: &mut [&mut Dynamic]) -> RhaiResult {
                         let arg0 = &mut args[0usize].write_lock::<u64>().unwrap();
@@ -1767,9 +1748,8 @@ mod generate_tests {
                 #[allow(unused_mut)]
                 #[doc(hidden)]
                 pub fn rhai_generate_into_module(m: &mut Module, flatten: bool) {
-                    m.set_fn("set$squared", FnNamespace::Global, FnAccess::Public, Some(int_foo_token::PARAM_NAMES),
-                             &[TypeId::of::<u64>(), TypeId::of::<u64>()],
-                             int_foo_token().into());
+                    FuncRegistration::new("set$squared").with_namespace(FnNamespace::Global).with_params_info(int_foo_token::PARAM_NAMES)
+                         .set_into_module_raw(m, &int_foo_token::param_types(), int_foo_token().into());
                     if flatten {} else {}
                 }
                 #[allow(non_camel_case_types)]
@@ -1780,7 +1760,7 @@ mod generate_tests {
                     pub const PARAM_NAMES: &'static [&'static str] = &["x: &mut u64", "y: u64", "()"];
                     #[inline(always)] pub fn param_types() -> [TypeId; 2usize] { [TypeId::of::<u64>(), TypeId::of::<u64>()] }
                 }
-                impl PluginFunction for int_foo_token {
+                impl PluginFunc for int_foo_token {
                     #[inline(always)]
                     fn call(&self, context: Option<NativeCallContext>, args: &mut [&mut Dynamic]) -> RhaiResult {
                         let arg1 = mem::take(args[1usize]).cast::<u64>();
@@ -1830,12 +1810,10 @@ mod generate_tests {
                 #[allow(unused_mut)]
                 #[doc(hidden)]
                 pub fn rhai_generate_into_module(m: &mut Module, flatten: bool) {
-                    m.set_fn("set_sq", FnNamespace::Internal, FnAccess::Public, Some(int_foo_token::PARAM_NAMES),
-                             &[TypeId::of::<u64>(), TypeId::of::<u64>()],
-                             int_foo_token().into());
-                    m.set_fn("set$squared", FnNamespace::Global, FnAccess::Public, Some(int_foo_token::PARAM_NAMES),
-                             &[TypeId::of::<u64>(), TypeId::of::<u64>()],
-                             int_foo_token().into());
+                    FuncRegistration::new("set_sq").with_namespace(FnNamespace::Internal).with_params_info(int_foo_token::PARAM_NAMES)
+                         .set_into_module_raw(m, &int_foo_token::param_types(), int_foo_token().into());
+                    FuncRegistration::new("set$squared").with_namespace(FnNamespace::Global).with_params_info(int_foo_token::PARAM_NAMES)
+                         .set_into_module_raw(m, &int_foo_token::param_types(), int_foo_token().into());
                     if flatten {} else {}
                 }
                 #[allow(non_camel_case_types)]
@@ -1846,7 +1824,7 @@ mod generate_tests {
                     pub const PARAM_NAMES: &'static [&'static str] = &["x: &mut u64", "y: u64", "()"];
                     #[inline(always)] pub fn param_types() -> [TypeId; 2usize] { [TypeId::of::<u64>(), TypeId::of::<u64>()] }
                 }
-                impl PluginFunction for int_foo_token {
+                impl PluginFunc for int_foo_token {
                     #[inline(always)]
                     fn call(&self, context: Option<NativeCallContext>, args: &mut [&mut Dynamic]) -> RhaiResult {
                         let arg1 = mem::take(args[1usize]).cast::<u64>();
@@ -1896,9 +1874,8 @@ mod generate_tests {
                 #[allow(unused_mut)]
                 #[doc(hidden)]
                 pub fn rhai_generate_into_module(m: &mut Module, flatten: bool) {
-                    m.set_fn("index$get$", FnNamespace::Global, FnAccess::Public, Some(get_by_index_token::PARAM_NAMES),
-                             &[TypeId::of::<MyCollection>(), TypeId::of::<u64>()],
-                             get_by_index_token().into());
+                    FuncRegistration::new("index$get$").with_namespace(FnNamespace::Global).with_params_info(get_by_index_token::PARAM_NAMES)
+                         .set_into_module_raw(m, &get_by_index_token::param_types(), get_by_index_token().into());
                     if flatten {} else {}
                 }
                 #[allow(non_camel_case_types)]
@@ -1909,7 +1886,7 @@ mod generate_tests {
                     pub const PARAM_NAMES: &'static [&'static str] = &["x: &mut MyCollection", "i: u64", "FLOAT"];
                     #[inline(always)] pub fn param_types() -> [TypeId; 2usize] { [TypeId::of::<MyCollection>(), TypeId::of::<u64>()] }
                 }
-                impl PluginFunction for get_by_index_token {
+                impl PluginFunc for get_by_index_token {
                     #[inline(always)]
                     fn call(&self, context: Option<NativeCallContext>, args: &mut [&mut Dynamic]) -> RhaiResult {
                         let arg1 = mem::take(args[1usize]).cast::<u64>();
@@ -1964,9 +1941,8 @@ mod generate_tests {
                 #[doc(hidden)]
                 pub fn rhai_generate_into_module(m: &mut Module, flatten: bool) {
                     #[cfg(hello)]
-                    m.set_fn("index$get$", FnNamespace::Global, FnAccess::Public, Some(get_by_index_token::PARAM_NAMES),
-                             &[TypeId::of::<MyCollection>(), TypeId::of::<u64>()],
-                             get_by_index_token().into());
+                    FuncRegistration::new("index$get$").with_namespace(FnNamespace::Global).with_params_info(get_by_index_token::PARAM_NAMES)
+                         .set_into_module_raw(m, &get_by_index_token::param_types(), get_by_index_token().into());
                     if flatten {} else {}
                 }
                 #[cfg(hello)]
@@ -1980,7 +1956,7 @@ mod generate_tests {
                     #[inline(always)] pub fn param_types() -> [TypeId; 2usize] { [TypeId::of::<MyCollection>(), TypeId::of::<u64>()] }
                 }
                 #[cfg(hello)]
-                impl PluginFunction for get_by_index_token {
+                impl PluginFunc for get_by_index_token {
                     #[inline(always)]
                     fn call(&self, context: Option<NativeCallContext>, args: &mut [&mut Dynamic]) -> RhaiResult {
                         let arg1 = mem::take(args[1usize]).cast::<u64>();
@@ -2030,12 +2006,10 @@ mod generate_tests {
                 #[allow(unused_mut)]
                 #[doc(hidden)]
                 pub fn rhai_generate_into_module(m: &mut Module, flatten: bool) {
-                    m.set_fn("get", FnNamespace::Internal, FnAccess::Public, Some(get_by_index_token::PARAM_NAMES),
-                             &[TypeId::of::<MyCollection>(), TypeId::of::<u64>()],
-                             get_by_index_token().into());
-                    m.set_fn("index$get$", FnNamespace::Global, FnAccess::Public, Some(get_by_index_token::PARAM_NAMES),
-                             &[TypeId::of::<MyCollection>(), TypeId::of::<u64>()],
-                             get_by_index_token().into());
+                    FuncRegistration::new("get").with_namespace(FnNamespace::Internal).with_params_info(get_by_index_token::PARAM_NAMES)
+                         .set_into_module_raw(m, &get_by_index_token::param_types(), get_by_index_token().into());
+                    FuncRegistration::new("index$get$").with_namespace(FnNamespace::Global).with_params_info(get_by_index_token::PARAM_NAMES)
+                         .set_into_module_raw(m, &get_by_index_token::param_types(), get_by_index_token().into());
                     if flatten {} else {}
                 }
                 #[allow(non_camel_case_types)]
@@ -2046,7 +2020,7 @@ mod generate_tests {
                     pub const PARAM_NAMES: &'static [&'static str] = &["x: &mut MyCollection", "i: u64", "FLOAT"];
                     #[inline(always)] pub fn param_types() -> [TypeId; 2usize] { [TypeId::of::<MyCollection>(), TypeId::of::<u64>()] }
                 }
-                impl PluginFunction for get_by_index_token {
+                impl PluginFunc for get_by_index_token {
                     #[inline(always)]
                     fn call(&self, context: Option<NativeCallContext>, args: &mut [&mut Dynamic]) -> RhaiResult {
                         let arg1 = mem::take(args[1usize]).cast::<u64>();
@@ -2096,9 +2070,8 @@ mod generate_tests {
                 #[allow(unused_mut)]
                 #[doc(hidden)]
                 pub fn rhai_generate_into_module(m: &mut Module, flatten: bool) {
-                    m.set_fn("index$set$", FnNamespace::Global, FnAccess::Public, Some(set_by_index_token::PARAM_NAMES),
-                             &[TypeId::of::<MyCollection>(), TypeId::of::<u64>(), TypeId::of::<FLOAT>()],
-                             set_by_index_token().into());
+                    FuncRegistration::new("index$set$").with_namespace(FnNamespace::Global).with_params_info(set_by_index_token::PARAM_NAMES)
+                         .set_into_module_raw(m, &set_by_index_token::param_types(), set_by_index_token().into());
                     if flatten {} else {}
                 }
                 #[allow(non_camel_case_types)]
@@ -2109,7 +2082,7 @@ mod generate_tests {
                     pub const PARAM_NAMES: &'static [&'static str] = &["x: &mut MyCollection", "i: u64", "item: FLOAT", "()"];
                     #[inline(always)] pub fn param_types() -> [TypeId; 3usize] { [TypeId::of::<MyCollection>(), TypeId::of::<u64>(), TypeId::of::<FLOAT>()] }
                 }
-                impl PluginFunction for set_by_index_token {
+                impl PluginFunc for set_by_index_token {
                     #[inline(always)]
                     fn call(&self, context: Option<NativeCallContext>, args: &mut [&mut Dynamic]) -> RhaiResult {
                         let arg1 = mem::take(args[1usize]).cast::<u64>();
@@ -2160,12 +2133,10 @@ mod generate_tests {
                 #[allow(unused_mut)]
                 #[doc(hidden)]
                 pub fn rhai_generate_into_module(m: &mut Module, flatten: bool) {
-                    m.set_fn("set", FnNamespace::Internal, FnAccess::Public, Some(set_by_index_token::PARAM_NAMES),
-                             &[TypeId::of::<MyCollection>(), TypeId::of::<u64>(), TypeId::of::<FLOAT>()],
-                             set_by_index_token().into());
-                    m.set_fn("index$set$", FnNamespace::Global, FnAccess::Public, Some(set_by_index_token::PARAM_NAMES),
-                             &[TypeId::of::<MyCollection>(), TypeId::of::<u64>(), TypeId::of::<FLOAT>()],
-                             set_by_index_token().into());
+                    FuncRegistration::new("set").with_namespace(FnNamespace::Internal).with_params_info(set_by_index_token::PARAM_NAMES)
+                         .set_into_module_raw(m, &set_by_index_token::param_types(), set_by_index_token().into());
+                    FuncRegistration::new("index$set$").with_namespace(FnNamespace::Global).with_params_info(set_by_index_token::PARAM_NAMES)
+                         .set_into_module_raw(m, &set_by_index_token::param_types(), set_by_index_token().into());
                     if flatten {} else {}
                 }
                 #[allow(non_camel_case_types)]
@@ -2176,7 +2147,7 @@ mod generate_tests {
                     pub const PARAM_NAMES: &'static [&'static str] = &["x: &mut MyCollection", "i: u64", "item: FLOAT", "()"];
                     #[inline(always)] pub fn param_types() -> [TypeId; 3usize] { [TypeId::of::<MyCollection>(), TypeId::of::<u64>(), TypeId::of::<FLOAT>()] }
                 }
-                impl PluginFunction for set_by_index_token {
+                impl PluginFunc for set_by_index_token {
                     #[inline(always)]
                     fn call(&self, context: Option<NativeCallContext>, args: &mut [&mut Dynamic]) -> RhaiResult {
                         let arg1 = mem::take(args[1usize]).cast::<u64>();
diff --git a/fuzz/clusterfuzz-testcase-fuzz_serde-4745120863813632 b/fuzz/clusterfuzz-testcase-fuzz_serde-4745120863813632
new file mode 100644
index 000000000..10677e9d5
Binary files /dev/null and b/fuzz/clusterfuzz-testcase-fuzz_serde-4745120863813632 differ
diff --git a/fuzz/clusterfuzz-testcase-scripting-4756460147900416 b/fuzz/clusterfuzz-testcase-scripting-4756460147900416
new file mode 100644
index 000000000..8ef14c69e
--- /dev/null
+++ b/fuzz/clusterfuzz-testcase-scripting-4756460147900416
@@ -0,0 +1 @@
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||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-+n-||||||||||||o;|||||oo|o|k|pppppn-||||||||||||o;|||||oo|o|k|pppppn-||||||||||||o;|||||oo|o|k|pppppp+o|k|pppppp+n-||||||||||||o;|||||oo|o|k|pppppn-||||||||||||o;||||-+n-||||||||||||o;|||||oo|o|k|pppppn-||||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||z|oo|o|k|pppppn-||||||||||||o;||||-+n-||||||||||||o;|||||oo|o|k|ppppp||||||||||||o;|||||oo|o|k|pppppn-||||||||||||o;|||||oo|o|k|pppppp+n-||||||||||||o;|||||oo|o|k|pppppn-||||||||||||o;||||-+n-||||||||||||o;|||||oo|o|k|pppppn-||||||||||||o;|||||oo|o|pk|ppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-+n-||||||||||||o;|||||oo|o|k|pppppn-||||||||||||o;|||||oo|o|k|pppppn-||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o||||o;||||-+n-||||||||||||o;|||||oo|o|k|ppppp||||||||||||o;|||||oo|o|k|pppppn-||||||||||||o;|||||oo|o|k|pppppp+n-||||||||||||o;|||||oo|o|k|pppppn-||||||||||||o;||||-+n-||||||||||||o;|||||oo|o|k|pppppn-||||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-+n-||||||||||||o;|||||oo|o|k|pppppn-||||||||||||o;|||||oo|o|k|pppppn-||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o||||o;||||-+n-||||||||||||o;|||||oo|o|k|ppppp||||||||||||o;|||||oo|o|k|pppppn-||||||||||||o;|||||oo|o|k|pppppp+n-||||||||||||o;|||||oo|o|k|pppppn-||||||||||||o;||||-+n-||||||||||||o;|||||oo|o|k|pppppn-||||||||||||o;|||||oo|o|k|pppppn-+n-||||||||||-||o;|||||oo|o|k|pppppn-||||||||||||o;||||-+n-||||||||||||o;|||||oo|o|k|pppppn-||||||||||||o;|||||oo|o|k|pppppn-||||||||||||o;|||||oo|o|k|pppppp+o|k|pppppp+n-||||||||||||o;|||||oo|o|k|ppp
\ No newline at end of file
diff --git a/src/api/build_type.rs b/src/api/build_type.rs
index 5b5e77a66..6d1e37a8a 100644
--- a/src/api/build_type.rs
+++ b/src/api/build_type.rs
@@ -1,7 +1,7 @@
 //! Trait to build a custom type for use with [`Engine`].
 use crate::func::SendSync;
 use crate::packages::string_basic::{FUNC_TO_DEBUG, FUNC_TO_STRING};
-use crate::{types::dynamic::Variant, Engine, Identifier, RegisterNativeFunction};
+use crate::{types::dynamic::Variant, Engine, Identifier, RhaiNativeFunc};
 use std::marker::PhantomData;
 #[cfg(feature = "no_std")]
 use std::prelude::v1::*;
@@ -98,13 +98,13 @@ impl Engine {
 ///
 /// To define a pretty-print name, call [`with_name`][`TypeBuilder::with_name`],
 /// to use [`Engine::register_type_with_name`] instead.
-pub struct TypeBuilder<'a, T: Variant + Clone> {
+pub struct TypeBuilder<'a, 's, T: Variant + Clone> {
     engine: &'a mut Engine,
-    name: Option<&'static str>,
+    name: Option<&'s str>,
     _marker: PhantomData<T>,
 }
 
-impl<'a, T: Variant + Clone> TypeBuilder<'a, T> {
+impl<'a, T: Variant + Clone> TypeBuilder<'a, '_, T> {
     /// Create a [`TypeBuilder`] linked to a particular [`Engine`] instance.
     #[inline(always)]
     fn new(engine: &'a mut Engine) -> Self {
@@ -116,11 +116,11 @@ impl<'a, T: Variant + Clone> TypeBuilder<'a, T> {
     }
 }
 
-impl<'a, T: Variant + Clone> TypeBuilder<'a, T> {
+impl<'s, T: Variant + Clone> TypeBuilder<'_, 's, T> {
     /// Set a pretty-print name for the `type_of` function.
     #[inline(always)]
-    pub fn with_name(&mut self, name: &'static str) -> &mut Self {
-        self.name = Some(name);
+    pub fn with_name(&mut self, name: &'s str) -> &mut Self {
+        self.name = Some(name.as_ref());
         self
     }
 
@@ -146,17 +146,17 @@ impl<'a, T: Variant + Clone> TypeBuilder<'a, T> {
 
     /// Register a custom function.
     #[inline(always)]
-    pub fn with_fn<A: 'static, const N: usize, const C: bool, R: Variant + Clone, const L: bool>(
+    pub fn with_fn<A: 'static, const N: usize, const X: bool, R: Variant + Clone, const F: bool>(
         &mut self,
         name: impl AsRef<str> + Into<Identifier>,
-        method: impl RegisterNativeFunction<A, N, C, R, L> + SendSync + 'static,
+        method: impl RhaiNativeFunc<A, N, X, R, F> + SendSync + 'static,
     ) -> &mut Self {
         self.engine.register_fn(name, method);
         self
     }
 }
 
-impl<'a, T> TypeBuilder<'a, T>
+impl<T> TypeBuilder<'_, '_, T>
 where
     T: Variant + Clone + IntoIterator,
     <T as IntoIterator>::Item: Variant + Clone,
@@ -171,17 +171,17 @@ where
 }
 
 #[cfg(not(feature = "no_object"))]
-impl<'a, T: Variant + Clone> TypeBuilder<'a, T> {
+impl<T: Variant + Clone> TypeBuilder<'_, '_, T> {
     /// Register a getter function.
     ///
     /// The function signature must start with `&mut self` and not `&self`.
     ///
     /// Not available under `no_object`.
     #[inline(always)]
-    pub fn with_get<const C: bool, V: Variant + Clone, const L: bool>(
+    pub fn with_get<const X: bool, R: Variant + Clone, const F: bool>(
         &mut self,
         name: impl AsRef<str>,
-        get_fn: impl RegisterNativeFunction<(Mut<T>,), 1, C, V, L> + SendSync + 'static,
+        get_fn: impl RhaiNativeFunc<(Mut<T>,), 1, X, R, F> + SendSync + 'static,
     ) -> &mut Self {
         self.engine.register_get(name, get_fn);
         self
@@ -191,10 +191,10 @@ impl<'a, T: Variant + Clone> TypeBuilder<'a, T> {
     ///
     /// Not available under `no_object`.
     #[inline(always)]
-    pub fn with_set<const C: bool, V: Variant + Clone, const L: bool>(
+    pub fn with_set<const X: bool, R: Variant + Clone, const F: bool>(
         &mut self,
         name: impl AsRef<str>,
-        set_fn: impl RegisterNativeFunction<(Mut<T>, V), 2, C, (), L> + SendSync + 'static,
+        set_fn: impl RhaiNativeFunc<(Mut<T>, R), 2, X, (), F> + SendSync + 'static,
     ) -> &mut Self {
         self.engine.register_set(name, set_fn);
         self
@@ -207,16 +207,16 @@ impl<'a, T: Variant + Clone> TypeBuilder<'a, T> {
     /// Not available under `no_object`.
     #[inline(always)]
     pub fn with_get_set<
-        const C1: bool,
-        const C2: bool,
-        V: Variant + Clone,
-        const L1: bool,
-        const L2: bool,
+        const X1: bool,
+        const X2: bool,
+        R: Variant + Clone,
+        const F1: bool,
+        const F2: bool,
     >(
         &mut self,
         name: impl AsRef<str>,
-        get_fn: impl RegisterNativeFunction<(Mut<T>,), 1, C1, V, L1> + SendSync + 'static,
-        set_fn: impl RegisterNativeFunction<(Mut<T>, V), 2, C2, (), L2> + SendSync + 'static,
+        get_fn: impl RhaiNativeFunc<(Mut<T>,), 1, X1, R, F1> + SendSync + 'static,
+        set_fn: impl RhaiNativeFunc<(Mut<T>, R), 2, X2, (), F2> + SendSync + 'static,
     ) -> &mut Self {
         self.engine.register_get_set(name, get_fn, set_fn);
         self
@@ -224,7 +224,7 @@ impl<'a, T: Variant + Clone> TypeBuilder<'a, T> {
 }
 
 #[cfg(any(not(feature = "no_index"), not(feature = "no_object")))]
-impl<'a, T: Variant + Clone> TypeBuilder<'a, T> {
+impl<T: Variant + Clone> TypeBuilder<'_, '_, T> {
     /// Register an index getter.
     ///
     /// The function signature must start with `&mut self` and not `&self`.
@@ -232,13 +232,13 @@ impl<'a, T: Variant + Clone> TypeBuilder<'a, T> {
     /// Not available under both `no_index` and `no_object`.
     #[inline(always)]
     pub fn with_indexer_get<
-        X: Variant + Clone,
-        const C: bool,
-        V: Variant + Clone,
-        const L: bool,
+        IDX: Variant + Clone,
+        const X: bool,
+        R: Variant + Clone,
+        const F: bool,
     >(
         &mut self,
-        get_fn: impl RegisterNativeFunction<(Mut<T>, X), 2, C, V, L> + SendSync + 'static,
+        get_fn: impl RhaiNativeFunc<(Mut<T>, IDX), 2, X, R, F> + SendSync + 'static,
     ) -> &mut Self {
         self.engine.register_indexer_get(get_fn);
         self
@@ -249,13 +249,13 @@ impl<'a, T: Variant + Clone> TypeBuilder<'a, T> {
     /// Not available under both `no_index` and `no_object`.
     #[inline(always)]
     pub fn with_indexer_set<
-        X: Variant + Clone,
-        const C: bool,
-        V: Variant + Clone,
-        const L: bool,
+        IDX: Variant + Clone,
+        const X: bool,
+        R: Variant + Clone,
+        const F: bool,
     >(
         &mut self,
-        set_fn: impl RegisterNativeFunction<(Mut<T>, X, V), 3, C, (), L> + SendSync + 'static,
+        set_fn: impl RhaiNativeFunc<(Mut<T>, IDX, R), 3, X, (), F> + SendSync + 'static,
     ) -> &mut Self {
         self.engine.register_indexer_set(set_fn);
         self
@@ -266,27 +266,27 @@ impl<'a, T: Variant + Clone> TypeBuilder<'a, T> {
     /// Not available under both `no_index` and `no_object`.
     #[inline(always)]
     pub fn with_indexer_get_set<
-        X: Variant + Clone,
-        const C1: bool,
-        const C2: bool,
-        V: Variant + Clone,
-        const L1: bool,
-        const L2: bool,
+        IDX: Variant + Clone,
+        const X1: bool,
+        const X2: bool,
+        R: Variant + Clone,
+        const F1: bool,
+        const F2: bool,
     >(
         &mut self,
-        get_fn: impl RegisterNativeFunction<(Mut<T>, X), 2, C1, V, L1> + SendSync + 'static,
-        set_fn: impl RegisterNativeFunction<(Mut<T>, X, V), 3, C2, (), L2> + SendSync + 'static,
+        get_fn: impl RhaiNativeFunc<(Mut<T>, IDX), 2, X1, R, F1> + SendSync + 'static,
+        set_fn: impl RhaiNativeFunc<(Mut<T>, IDX, R), 3, X2, (), F2> + SendSync + 'static,
     ) -> &mut Self {
         self.engine.register_indexer_get_set(get_fn, set_fn);
         self
     }
 }
 
-impl<'a, T: Variant + Clone> Drop for TypeBuilder<'a, T> {
+impl<T: Variant + Clone> Drop for TypeBuilder<'_, '_, T> {
     #[inline]
     fn drop(&mut self) {
         match self.name {
-            Some(name) => self.engine.register_type_with_name::<T>(name),
+            Some(ref name) => self.engine.register_type_with_name::<T>(name),
             None => self.engine.register_type::<T>(),
         };
     }
diff --git a/src/api/definitions/mod.rs b/src/api/definitions/mod.rs
index abd373804..2d7391f08 100644
--- a/src/api/definitions/mod.rs
+++ b/src/api/definitions/mod.rs
@@ -2,7 +2,7 @@
 #![cfg(feature = "internals")]
 #![cfg(feature = "metadata")]
 
-use crate::module::{FuncInfo, ModuleFlags};
+use crate::module::{FuncMetadata, ModuleFlags};
 use crate::tokenizer::{is_valid_function_name, Token};
 use crate::{Engine, FnAccess, FnPtr, Module, Scope, INT};
 
@@ -436,29 +436,26 @@ impl Module {
         }
 
         let mut func_infos = self.iter_fn().collect::<Vec<_>>();
-        func_infos.sort_by(|a, b| match a.metadata.name.cmp(&b.metadata.name) {
-            Ordering::Equal => match a.metadata.num_params.cmp(&b.metadata.num_params) {
-                Ordering::Equal => (a.metadata.params_info.join("")
-                    + a.metadata.return_type.as_str())
-                .cmp(&(b.metadata.params_info.join("") + b.metadata.return_type.as_str())),
+        func_infos.sort_by(|(_, a), (_, b)| match a.name.cmp(&b.name) {
+            Ordering::Equal => match a.num_params.cmp(&b.num_params) {
+                Ordering::Equal => (a.params_info.join("") + a.return_type.as_str())
+                    .cmp(&(b.params_info.join("") + b.return_type.as_str())),
                 o => o,
             },
             o => o,
         });
 
-        for f in func_infos {
+        for (_, f) in func_infos {
             if !first {
                 writer.write_str("\n\n")?;
             }
             first = false;
 
-            if f.metadata.access != FnAccess::Private {
-                let operator =
-                    !f.metadata.name.contains('$') && !is_valid_function_name(&f.metadata.name);
+            if f.access != FnAccess::Private {
+                let operator = !f.name.contains('$') && !is_valid_function_name(&f.name);
 
                 #[cfg(not(feature = "no_custom_syntax"))]
-                let operator =
-                    operator || def.engine.custom_keywords.contains_key(&f.metadata.name);
+                let operator = operator || def.engine.custom_keywords.contains_key(&f.name);
 
                 f.write_definition(writer, def, operator)?;
             }
@@ -468,7 +465,7 @@ impl Module {
     }
 }
 
-impl FuncInfo {
+impl FuncMetadata {
     /// Output definitions for a function.
     fn write_definition(
         &self,
@@ -476,7 +473,7 @@ impl FuncInfo {
         def: &Definitions,
         operator: bool,
     ) -> fmt::Result {
-        for comment in &*self.metadata.comments {
+        for comment in &*self.comments {
             writeln!(writer, "{comment}")?;
         }
 
@@ -486,33 +483,29 @@ impl FuncInfo {
             writer.write_str("fn ")?;
         }
 
-        if let Some(name) = self.metadata.name.strip_prefix("get$") {
+        if let Some(name) = self.name.strip_prefix("get$") {
             write!(writer, "get {name}(")?;
-        } else if let Some(name) = self.metadata.name.strip_prefix("set$") {
+        } else if let Some(name) = self.name.strip_prefix("set$") {
             write!(writer, "set {name}(")?;
         } else {
-            write!(writer, "{}(", self.metadata.name)?;
+            write!(writer, "{}(", self.name)?;
         }
 
         let mut first = true;
-        for i in 0..self.metadata.num_params {
+        for i in 0..self.num_params {
             if !first {
                 writer.write_str(", ")?;
             }
             first = false;
 
-            let (param_name, param_type) =
-                self.metadata
-                    .params_info
-                    .get(i)
-                    .map_or(("_", "?".into()), |s| {
-                        let mut s = s.splitn(2, ':');
-                        (
-                            s.next().unwrap_or("_").split(' ').last().unwrap(),
-                            s.next()
-                                .map_or(Cow::Borrowed("?"), |ty| def_type_name(ty, def.engine)),
-                        )
-                    });
+            let (param_name, param_type) = self.params_info.get(i).map_or(("_", "?".into()), |s| {
+                let mut s = s.splitn(2, ':');
+                (
+                    s.next().unwrap_or("_").split(' ').last().unwrap(),
+                    s.next()
+                        .map_or(Cow::Borrowed("?"), |ty| def_type_name(ty, def.engine)),
+                )
+            });
 
             if operator {
                 write!(writer, "{param_type}")?;
@@ -524,7 +517,7 @@ impl FuncInfo {
         write!(
             writer,
             ") -> {};",
-            def_type_name(&self.metadata.return_type, def.engine)
+            def_type_name(&self.return_type, def.engine)
         )?;
 
         Ok(())
diff --git a/src/api/deprecated.rs b/src/api/deprecated.rs
index 2e2aec065..17248b62c 100644
--- a/src/api/deprecated.rs
+++ b/src/api/deprecated.rs
@@ -1,12 +1,13 @@
 //! Module containing all deprecated API that will be removed in the next major version.
 
-use crate::func::SendSync;
+use crate::func::{RhaiFunc, SendSync};
 use crate::types::dynamic::Variant;
 use crate::{
-    Dynamic, Engine, EvalAltResult, FnPtr, Identifier, ImmutableString, Module, NativeCallContext,
-    Position, RegisterNativeFunction, RhaiResult, RhaiResultOf, Scope, SharedModule, TypeBuilder,
-    AST,
+    Dynamic, Engine, EvalAltResult, FnAccess, FnNamespace, FnPtr, FuncRegistration, Identifier,
+    ImmutableString, Module, NativeCallContext, Position, RhaiNativeFunc, RhaiResult, RhaiResultOf,
+    Scope, SharedModule, TypeBuilder, AST,
 };
+use std::any::TypeId;
 #[cfg(feature = "no_std")]
 use std::prelude::v1::*;
 
@@ -195,10 +196,10 @@ impl Engine {
     /// This method will be removed in the next major version.
     #[deprecated(since = "1.9.1", note = "use `register_fn` instead")]
     #[inline(always)]
-    pub fn register_result_fn<A: 'static, const N: usize, const C: bool, R: Variant + Clone>(
+    pub fn register_result_fn<A: 'static, const N: usize, const X: bool, R: Variant + Clone>(
         &mut self,
         name: impl AsRef<str> + Into<Identifier>,
-        func: impl RegisterNativeFunction<A, N, C, R, true> + SendSync + 'static,
+        func: impl RhaiNativeFunc<A, N, X, R, true> + SendSync + 'static,
     ) -> &mut Self {
         self.register_fn(name, func)
     }
@@ -217,10 +218,10 @@ impl Engine {
     #[deprecated(since = "1.9.1", note = "use `register_get` instead")]
     #[cfg(not(feature = "no_object"))]
     #[inline(always)]
-    pub fn register_get_result<T: Variant + Clone, const C: bool, V: Variant + Clone>(
+    pub fn register_get_result<T: Variant + Clone, const X: bool, R: Variant + Clone>(
         &mut self,
         name: impl AsRef<str>,
-        get_fn: impl RegisterNativeFunction<(Mut<T>,), 1, C, V, true> + SendSync + 'static,
+        get_fn: impl RhaiNativeFunc<(Mut<T>,), 1, X, R, true> + SendSync + 'static,
     ) -> &mut Self {
         self.register_get(name, get_fn)
     }
@@ -237,10 +238,10 @@ impl Engine {
     #[deprecated(since = "1.9.1", note = "use `register_set` instead")]
     #[cfg(not(feature = "no_object"))]
     #[inline(always)]
-    pub fn register_set_result<T: Variant + Clone, V: Variant + Clone, const C: bool, S>(
+    pub fn register_set_result<T: Variant + Clone, V: Variant + Clone, const X: bool>(
         &mut self,
         name: impl AsRef<str>,
-        set_fn: impl RegisterNativeFunction<(Mut<T>, V), 2, C, (), true> + SendSync + 'static,
+        set_fn: impl RhaiNativeFunc<(Mut<T>, V), 2, X, (), true> + SendSync + 'static,
     ) -> &mut Self {
         self.register_set(name, set_fn)
     }
@@ -261,12 +262,12 @@ impl Engine {
     #[inline(always)]
     pub fn register_indexer_get_result<
         T: Variant + Clone,
-        X: Variant + Clone,
-        V: Variant + Clone,
-        const C: bool,
+        IDX: Variant + Clone,
+        R: Variant + Clone,
+        const X: bool,
     >(
         &mut self,
-        get_fn: impl RegisterNativeFunction<(Mut<T>, X), 2, C, V, true> + SendSync + 'static,
+        get_fn: impl RhaiNativeFunc<(Mut<T>, IDX), 2, X, R, true> + SendSync + 'static,
     ) -> &mut Self {
         self.register_indexer_get(get_fn)
     }
@@ -285,12 +286,12 @@ impl Engine {
     #[inline(always)]
     pub fn register_indexer_set_result<
         T: Variant + Clone,
-        X: Variant + Clone,
-        V: Variant + Clone,
-        const C: bool,
+        IDX: Variant + Clone,
+        R: Variant + Clone,
+        const X: bool,
     >(
         &mut self,
-        set_fn: impl RegisterNativeFunction<(Mut<T>, X, V), 3, C, (), true> + SendSync + 'static,
+        set_fn: impl RhaiNativeFunc<(Mut<T>, IDX, R), 3, X, (), true> + SendSync + 'static,
     ) -> &mut Self {
         self.register_indexer_set(set_fn)
     }
@@ -550,7 +551,7 @@ impl Position {
 }
 
 #[allow(deprecated)]
-impl<'a, T: Variant + Clone> TypeBuilder<'a, T> {
+impl<T: Variant + Clone> TypeBuilder<'_, '_, T> {
     /// Register a custom fallible function.
     ///
     /// # Deprecated
@@ -561,15 +562,15 @@ impl<'a, T: Variant + Clone> TypeBuilder<'a, T> {
     /// This method will be removed in the next major version.
     #[deprecated(since = "1.9.1", note = "use `with_fn` instead")]
     #[inline(always)]
-    pub fn with_result_fn<S, A: 'static, const N: usize, const C: bool, R, F>(
+    pub fn with_result_fn<S, A: 'static, const N: usize, const X: bool, R, FUNC>(
         &mut self,
         name: S,
-        method: F,
+        method: FUNC,
     ) -> &mut Self
     where
         S: AsRef<str> + Into<Identifier>,
         R: Variant + Clone,
-        F: RegisterNativeFunction<A, N, C, R, true> + SendSync + 'static,
+        FUNC: RhaiNativeFunc<A, N, X, R, true> + SendSync + 'static,
     {
         self.with_fn(name, method)
     }
@@ -589,10 +590,10 @@ impl<'a, T: Variant + Clone> TypeBuilder<'a, T> {
     #[deprecated(since = "1.9.1", note = "use `with_get` instead")]
     #[cfg(not(feature = "no_object"))]
     #[inline(always)]
-    pub fn with_get_result<V: Variant + Clone, const C: bool>(
+    pub fn with_get_result<const X: bool, R: Variant + Clone>(
         &mut self,
         name: impl AsRef<str>,
-        get_fn: impl RegisterNativeFunction<(Mut<T>,), 1, C, V, true> + SendSync + 'static,
+        get_fn: impl RhaiNativeFunc<(Mut<T>,), 1, X, R, true> + SendSync + 'static,
     ) -> &mut Self {
         self.with_get(name, get_fn)
     }
@@ -610,10 +611,10 @@ impl<'a, T: Variant + Clone> TypeBuilder<'a, T> {
     #[deprecated(since = "1.9.1", note = "use `with_set` instead")]
     #[cfg(not(feature = "no_object"))]
     #[inline(always)]
-    pub fn with_set_result<V: Variant + Clone, const C: bool>(
+    pub fn with_set_result<const X: bool, R: Variant + Clone>(
         &mut self,
         name: impl AsRef<str>,
-        set_fn: impl RegisterNativeFunction<(Mut<T>, V), 2, C, (), true> + SendSync + 'static,
+        set_fn: impl RhaiNativeFunc<(Mut<T>, R), 2, X, (), true> + SendSync + 'static,
     ) -> &mut Self {
         self.with_set(name, set_fn)
     }
@@ -633,9 +634,9 @@ impl<'a, T: Variant + Clone> TypeBuilder<'a, T> {
     #[deprecated(since = "1.9.1", note = "use `with_indexer_get` instead")]
     #[cfg(any(not(feature = "no_index"), not(feature = "no_object")))]
     #[inline(always)]
-    pub fn with_indexer_get_result<X: Variant + Clone, V: Variant + Clone, const C: bool>(
+    pub fn with_indexer_get_result<IDX: Variant + Clone, R: Variant + Clone, const X: bool>(
         &mut self,
-        get_fn: impl RegisterNativeFunction<(Mut<T>, X), 2, C, V, true> + SendSync + 'static,
+        get_fn: impl RhaiNativeFunc<(Mut<T>, IDX), 2, X, R, true> + SendSync + 'static,
     ) -> &mut Self {
         self.with_indexer_get(get_fn)
     }
@@ -653,9 +654,9 @@ impl<'a, T: Variant + Clone> TypeBuilder<'a, T> {
     #[deprecated(since = "1.9.1", note = "use `with_indexer_set` instead")]
     #[cfg(any(not(feature = "no_index"), not(feature = "no_object")))]
     #[inline(always)]
-    pub fn with_indexer_set_result<X: Variant + Clone, V: Variant + Clone, const C: bool>(
+    pub fn with_indexer_set_result<IDX: Variant + Clone, R: Variant + Clone, const X: bool>(
         &mut self,
-        set_fn: impl RegisterNativeFunction<(Mut<T>, X, V), 3, C, (), true> + SendSync + 'static,
+        set_fn: impl RhaiNativeFunc<(Mut<T>, IDX, R), 3, X, (), true> + SendSync + 'static,
     ) -> &mut Self {
         self.with_indexer_set(set_fn)
     }
@@ -694,6 +695,99 @@ impl Module {
     pub fn get_custom_type(&self, type_name: &str) -> Option<&str> {
         self.get_custom_type_display_by_name(type_name)
     }
+
+    /// Set a native Rust function into the [`Module`], returning a [`u64`] hash key.
+    ///
+    /// If there is an existing Rust function of the same hash, it is replaced.
+    ///
+    /// # Deprecated
+    ///
+    /// This method is deprecated.
+    /// Use the [`FuncRegistration`] API instead.
+    ///
+    /// This method will be removed in the next major version.
+    #[deprecated(since = "1.17.0", note = "use the `FuncRegistration` API instead")]
+    #[inline(always)]
+    pub fn set_fn(
+        &mut self,
+        name: impl Into<Identifier>,
+        namespace: FnNamespace,
+        _access: FnAccess,
+        arg_names: Option<&[&str]>,
+        arg_types: impl AsRef<[TypeId]>,
+        func: RhaiFunc,
+    ) -> u64 {
+        let _arg_names = arg_names;
+
+        let fx = FuncRegistration::new(name).with_namespace(namespace);
+
+        #[cfg(feature = "metadata")]
+        let fx = if let Some(arg_names) = _arg_names {
+            fx.with_params_info(arg_names)
+        } else {
+            fx
+        };
+
+        fx.set_into_module_raw(self, arg_types, func).hash
+    }
+
+    /// _(metadata)_ Set a native Rust function into the [`Module`], returning a [`u64`] hash key.
+    /// Exported under the `metadata` feature only.
+    ///
+    /// If there is an existing Rust function of the same hash, it is replaced.
+    ///
+    /// # Deprecated
+    ///
+    /// This method is deprecated.
+    /// Use the [`FuncRegistration`] API instead.
+    ///
+    /// This method will be removed in the next major version.
+    #[deprecated(since = "1.17.0", note = "use the `FuncRegistration` API instead")]
+    #[cfg(feature = "metadata")]
+    #[inline(always)]
+    pub fn set_fn_with_comments<C: AsRef<str>>(
+        &mut self,
+        name: impl Into<Identifier>,
+        namespace: FnNamespace,
+        _access: FnAccess,
+        arg_names: Option<&[&str]>,
+        arg_types: impl AsRef<[TypeId]>,
+        comments: impl IntoIterator<Item = C>,
+        func: RhaiFunc,
+    ) -> u64 {
+        FuncRegistration::new(name)
+            .with_namespace(namespace)
+            .with_params_info(arg_names.unwrap_or(&[]))
+            .with_comments(comments)
+            .set_into_module_raw(self, arg_types, func)
+            .hash
+    }
+
+    /// _(metadata)_ Update the metadata (parameter names/types and return type) of a registered function.
+    /// Exported under the `metadata` feature only.
+    ///
+    /// The [`u64`] hash is returned by the [`set_native_fn`][Module::set_native_fn] call.
+    ///
+    /// # Deprecated
+    ///
+    /// This method is deprecated.
+    /// Use [`update_fn_metadata_with_comments`][`Module::update_fn_metadata_with_comments`] instead.
+    ///
+    /// This method will be removed in the next major version.
+    #[deprecated(
+        since = "1.17.0",
+        note = "use `update_fn_metadata_with_comments` instead"
+    )]
+    #[cfg(feature = "metadata")]
+    #[inline(always)]
+    #[allow(deprecated)]
+    pub fn update_fn_metadata<S: Into<Identifier>>(
+        &mut self,
+        hash_fn: u64,
+        arg_names: impl IntoIterator<Item = S>,
+    ) -> &mut Self {
+        self.update_fn_metadata_with_comments(hash_fn, arg_names, [""; 0])
+    }
 }
 
 #[cfg(not(feature = "no_index"))]
diff --git a/src/api/limits.rs b/src/api/limits.rs
index e03c624b7..c561ba372 100644
--- a/src/api/limits.rs
+++ b/src/api/limits.rs
@@ -62,6 +62,13 @@ pub struct Limits {
     ///
     /// Set to zero to effectively disable creating variables.
     pub num_variables: usize,
+    /// Maximum number of scripted functions allowed.
+    ///
+    /// Set to zero to effectively disable defining any function.
+    ///
+    /// Not available under `no_function`.
+    #[cfg(not(feature = "no_function"))]
+    pub num_functions: usize,
     /// Maximum number of [modules][crate::Module] allowed to load.
     ///
     /// Set to zero to effectively disable loading any [module][crate::Module].
@@ -97,6 +104,8 @@ impl Limits {
             function_expr_depth: NonZeroUsize::new(default_limits::MAX_FUNCTION_EXPR_DEPTH),
             num_operations: None,
             num_variables: usize::MAX,
+            #[cfg(not(feature = "no_function"))]
+            num_functions: usize::MAX,
             #[cfg(not(feature = "no_module"))]
             num_modules: usize::MAX,
             string_len: None,
@@ -151,13 +160,11 @@ impl Engine {
     /// The maximum levels of function calls allowed for a script.
     ///
     /// Not available under `unchecked` or `no_function`.
+    #[cfg(not(feature = "no_function"))]
     #[inline(always)]
     #[must_use]
     pub const fn max_call_levels(&self) -> usize {
-        #[cfg(not(feature = "no_function"))]
-        return self.limits.call_stack_depth;
-        #[cfg(feature = "no_function")]
-        return 0;
+        self.limits.call_stack_depth
     }
     /// Set the maximum number of operations allowed for a script to run to avoid
     /// consuming too much resources (0 for unlimited).
@@ -179,15 +186,15 @@ impl Engine {
             None => 0,
         }
     }
-    /// Set the maximum number of imported variables allowed for a script at any instant.
+    /// Set the maximum number of variables allowed for a script at any instant.
     ///
     /// Not available under `unchecked`.
     #[inline(always)]
-    pub fn set_max_variables(&mut self, modules: usize) -> &mut Self {
-        self.limits.num_variables = modules;
+    pub fn set_max_variables(&mut self, variables: usize) -> &mut Self {
+        self.limits.num_variables = variables;
         self
     }
-    /// The maximum number of imported variables allowed for a script at any instant.
+    /// The maximum number of variables allowed for a script at any instant.
     ///
     /// Not available under `unchecked`.
     #[inline(always)]
@@ -195,6 +202,24 @@ impl Engine {
     pub const fn max_variables(&self) -> usize {
         self.limits.num_variables
     }
+    /// Set the maximum number of scripted functions allowed for a script at any instant.
+    ///
+    /// Not available under `unchecked` or `no_function`
+    #[cfg(not(feature = "no_function"))]
+    #[inline(always)]
+    pub fn set_max_functions(&mut self, functions: usize) -> &mut Self {
+        self.limits.num_functions = functions;
+        self
+    }
+    /// The maximum number of scripted functions allowed for a script at any instant.
+    ///
+    /// Not available under `unchecked` or `no_function`
+    #[cfg(not(feature = "no_function"))]
+    #[inline(always)]
+    #[must_use]
+    pub const fn max_functions(&self) -> usize {
+        self.limits.num_functions
+    }
     /// Set the maximum number of imported [modules][crate::Module] allowed for a script.
     ///
     /// Not available under `unchecked` or `no_module`.
@@ -207,13 +232,11 @@ impl Engine {
     /// The maximum number of imported [modules][crate::Module] allowed for a script.
     ///
     /// Not available under `unchecked` or `no_module`.
+    #[cfg(not(feature = "no_module"))]
     #[inline(always)]
     #[must_use]
     pub const fn max_modules(&self) -> usize {
-        #[cfg(not(feature = "no_module"))]
-        return self.limits.num_modules;
-        #[cfg(feature = "no_module")]
-        return 0;
+        self.limits.num_modules
     }
     /// Set the depth limits for expressions (0 for unlimited).
     ///
diff --git a/src/api/optimize.rs b/src/api/optimize.rs
index 28b4ac971..59db8c261 100644
--- a/src/api/optimize.rs
+++ b/src/api/optimize.rs
@@ -58,7 +58,7 @@ impl Engine {
             #[cfg(not(feature = "no_function"))]
             ast.shared_lib()
                 .iter_fn()
-                .map(|f| f.func.get_script_fn_def().cloned().expect("`ScriptFnDef`"))
+                .map(|(f, _)| f.get_script_fn_def().cloned().expect("`ScriptFuncDef`"))
                 .collect(),
             optimization_level,
         );
diff --git a/src/api/register.rs b/src/api/register.rs
index 794905a8e..9b25c0b39 100644
--- a/src/api/register.rs
+++ b/src/api/register.rs
@@ -1,10 +1,10 @@
 //! Module that defines the public function/module registration API of [`Engine`].
 
-use crate::func::{FnCallArgs, RegisterNativeFunction, SendSync};
-use crate::module::ModuleFlags;
+use crate::func::{FnCallArgs, RhaiFunc, RhaiNativeFunc, SendSync};
+use crate::module::{FuncRegistration, ModuleFlags};
 use crate::types::dynamic::Variant;
 use crate::{
-    Engine, FnAccess, FnNamespace, Identifier, Module, NativeCallContext, RhaiResultOf, Shared,
+    Dynamic, Engine, FnNamespace, Identifier, Module, NativeCallContext, RhaiResultOf, Shared,
     SharedModule,
 };
 use std::any::{type_name, TypeId};
@@ -64,26 +64,26 @@ impl Engine {
     pub fn register_fn<
         A: 'static,
         const N: usize,
-        const C: bool,
+        const X: bool,
         R: Variant + Clone,
-        const L: bool,
-        F: RegisterNativeFunction<A, N, C, R, L> + SendSync + 'static,
+        const F: bool,
+        FUNC: RhaiNativeFunc<A, N, X, R, F> + SendSync + 'static,
     >(
         &mut self,
         name: impl AsRef<str> + Into<Identifier>,
-        func: F,
+        func: FUNC,
     ) -> &mut Self {
-        let param_types = F::param_types();
+        let param_types = FUNC::param_types();
 
         #[cfg(feature = "metadata")]
-        let mut param_type_names = F::param_names()
+        let mut param_type_names = FUNC::param_names()
             .iter()
             .map(|ty| format!("_: {}", self.format_type_name(ty)))
             .collect::<crate::FnArgsVec<_>>();
 
         #[cfg(feature = "metadata")]
-        if F::return_type() != TypeId::of::<()>() {
-            param_type_names.push(self.format_type_name(F::return_type_name()).into());
+        if FUNC::return_type() != TypeId::of::<()>() {
+            param_type_names.push(self.format_type_name(FUNC::return_type_name()).into());
         }
 
         #[cfg(feature = "metadata")]
@@ -91,31 +91,27 @@ impl Engine {
             .iter()
             .map(String::as_str)
             .collect::<crate::FnArgsVec<_>>();
-        #[cfg(feature = "metadata")]
-        let param_type_names = Some(param_type_names.as_ref());
-
-        #[cfg(not(feature = "metadata"))]
-        let param_type_names: Option<&[&str]> = None;
 
-        let fn_name = name.as_ref();
+        let fn_name = name.into();
         let is_pure = true;
 
         #[cfg(any(not(feature = "no_index"), not(feature = "no_object")))]
-        let is_pure = is_pure && (F::num_params() != 3 || fn_name != crate::engine::FN_IDX_SET);
+        let is_pure = is_pure && (FUNC::num_params() != 3 || fn_name != crate::engine::FN_IDX_SET);
         #[cfg(not(feature = "no_object"))]
         let is_pure =
-            is_pure && (F::num_params() != 2 || !fn_name.starts_with(crate::engine::FN_SET));
+            is_pure && (FUNC::num_params() != 2 || !fn_name.starts_with(crate::engine::FN_SET));
+
+        let f = FuncRegistration::new(fn_name).with_namespace(FnNamespace::Global);
 
-        let func = func.into_callable_function(fn_name.into(), is_pure, true);
+        #[cfg(feature = "metadata")]
+        let f = f.with_params_info(param_type_names);
 
-        self.global_namespace_mut().set_fn(
-            name,
-            FnNamespace::Global,
-            FnAccess::Public,
-            param_type_names,
+        f.set_into_module_raw(
+            self.global_namespace_mut(),
             param_types,
-            func,
+            func.into_callable_function(is_pure, true),
         );
+
         self
     }
     /// Register a function of the [`Engine`].
@@ -143,13 +139,23 @@ impl Engine {
         arg_types: impl AsRef<[TypeId]>,
         func: impl Fn(NativeCallContext, &mut FnCallArgs) -> RhaiResultOf<T> + SendSync + 'static,
     ) -> &mut Self {
-        self.global_namespace_mut().set_raw_fn(
-            name,
-            FnNamespace::Global,
-            FnAccess::Public,
-            arg_types,
-            func,
-        );
+        FuncRegistration::new(name)
+            .with_namespace(FnNamespace::Global)
+            .set_into_module_raw(
+                self.global_namespace_mut(),
+                arg_types,
+                RhaiFunc::Method {
+                    func: Shared::new(
+                        move |ctx: Option<NativeCallContext>, args: &mut FnCallArgs| {
+                            func(ctx.unwrap(), args).map(Dynamic::from)
+                        },
+                    ),
+                    has_context: true,
+                    is_pure: false,
+                    is_volatile: true,
+                },
+            );
+
         self
     }
     /// Register a custom type for use with the [`Engine`].
@@ -274,12 +280,12 @@ impl Engine {
     /// Register a fallible type iterator for an iterable type with the [`Engine`].
     /// This is an advanced API.
     #[inline(always)]
-    pub fn register_iterator_result<T, X>(&mut self) -> &mut Self
+    pub fn register_iterator_result<T, R>(&mut self) -> &mut Self
     where
-        T: Variant + Clone + IntoIterator<Item = RhaiResultOf<X>>,
-        X: Variant + Clone,
+        T: Variant + Clone + IntoIterator<Item = RhaiResultOf<R>>,
+        R: Variant + Clone,
     {
-        self.global_namespace_mut().set_iterable_result::<T, X>();
+        self.global_namespace_mut().set_iterable_result::<T, R>();
         self
     }
     /// Register a getter function for a member of a registered type with the [`Engine`].
@@ -324,10 +330,10 @@ impl Engine {
     /// ```
     #[cfg(not(feature = "no_object"))]
     #[inline(always)]
-    pub fn register_get<T: Variant + Clone, const C: bool, V: Variant + Clone, const L: bool>(
+    pub fn register_get<T: Variant + Clone, const X: bool, R: Variant + Clone, const F: bool>(
         &mut self,
         name: impl AsRef<str>,
-        get_fn: impl RegisterNativeFunction<(Mut<T>,), 1, C, V, L> + SendSync + 'static,
+        get_fn: impl RhaiNativeFunc<(Mut<T>,), 1, X, R, F> + SendSync + 'static,
     ) -> &mut Self {
         self.register_fn(crate::engine::make_getter(name.as_ref()), get_fn)
     }
@@ -374,10 +380,10 @@ impl Engine {
     /// ```
     #[cfg(not(feature = "no_object"))]
     #[inline(always)]
-    pub fn register_set<T: Variant + Clone, const C: bool, V: Variant + Clone, const L: bool>(
+    pub fn register_set<T: Variant + Clone, const X: bool, R: Variant + Clone, const F: bool>(
         &mut self,
         name: impl AsRef<str>,
-        set_fn: impl RegisterNativeFunction<(Mut<T>, V), 2, C, (), L> + SendSync + 'static,
+        set_fn: impl RhaiNativeFunc<(Mut<T>, R), 2, X, (), F> + SendSync + 'static,
     ) -> &mut Self {
         self.register_fn(crate::engine::make_setter(name.as_ref()), set_fn)
     }
@@ -430,16 +436,16 @@ impl Engine {
     #[inline(always)]
     pub fn register_get_set<
         T: Variant + Clone,
-        const C1: bool,
-        const C2: bool,
-        V: Variant + Clone,
-        const L1: bool,
-        const L2: bool,
+        const X1: bool,
+        const X2: bool,
+        R: Variant + Clone,
+        const F1: bool,
+        const F2: bool,
     >(
         &mut self,
         name: impl AsRef<str>,
-        get_fn: impl RegisterNativeFunction<(Mut<T>,), 1, C1, V, L1> + SendSync + 'static,
-        set_fn: impl RegisterNativeFunction<(Mut<T>, V), 2, C2, (), L2> + SendSync + 'static,
+        get_fn: impl RhaiNativeFunc<(Mut<T>,), 1, X1, R, F1> + SendSync + 'static,
+        set_fn: impl RhaiNativeFunc<(Mut<T>, R), 2, X2, (), F2> + SendSync + 'static,
     ) -> &mut Self {
         self.register_get(&name, get_fn).register_set(&name, set_fn)
     }
@@ -496,13 +502,13 @@ impl Engine {
     #[inline]
     pub fn register_indexer_get<
         T: Variant + Clone,
-        X: Variant + Clone,
-        const C: bool,
-        V: Variant + Clone,
-        const L: bool,
+        IDX: Variant + Clone,
+        const X: bool,
+        R: Variant + Clone,
+        const F: bool,
     >(
         &mut self,
-        get_fn: impl RegisterNativeFunction<(Mut<T>, X), 2, C, V, L> + SendSync + 'static,
+        get_fn: impl RhaiNativeFunc<(Mut<T>, IDX), 2, X, R, F> + SendSync + 'static,
     ) -> &mut Self {
         #[cfg(not(feature = "no_index"))]
         assert!(
@@ -583,13 +589,13 @@ impl Engine {
     #[inline]
     pub fn register_indexer_set<
         T: Variant + Clone,
-        X: Variant + Clone,
-        const C: bool,
-        V: Variant + Clone,
-        const L: bool,
+        IDX: Variant + Clone,
+        const X: bool,
+        R: Variant + Clone,
+        const F: bool,
     >(
         &mut self,
-        set_fn: impl RegisterNativeFunction<(Mut<T>, X, V), 3, C, (), L> + SendSync + 'static,
+        set_fn: impl RhaiNativeFunc<(Mut<T>, IDX, R), 3, X, (), F> + SendSync + 'static,
     ) -> &mut Self {
         #[cfg(not(feature = "no_index"))]
         assert!(
@@ -671,16 +677,16 @@ impl Engine {
     #[inline(always)]
     pub fn register_indexer_get_set<
         T: Variant + Clone,
-        X: Variant + Clone,
-        const C1: bool,
-        const C2: bool,
-        V: Variant + Clone,
-        const L1: bool,
-        const L2: bool,
+        IDX: Variant + Clone,
+        const X1: bool,
+        const X2: bool,
+        R: Variant + Clone,
+        const F1: bool,
+        const F2: bool,
     >(
         &mut self,
-        get_fn: impl RegisterNativeFunction<(Mut<T>, X), 2, C1, V, L1> + SendSync + 'static,
-        set_fn: impl RegisterNativeFunction<(Mut<T>, X, V), 3, C2, (), L2> + SendSync + 'static,
+        get_fn: impl RhaiNativeFunc<(Mut<T>, IDX), 2, X1, R, F1> + SendSync + 'static,
+        set_fn: impl RhaiNativeFunc<(Mut<T>, IDX, R), 3, X2, (), F2> + SendSync + 'static,
     ) -> &mut Self {
         self.register_indexer_get(get_fn)
             .register_indexer_set(set_fn)
diff --git a/src/ast/ast.rs b/src/ast/ast.rs
index 681378838..9a2444970 100644
--- a/src/ast/ast.rs
+++ b/src/ast/ast.rs
@@ -11,6 +11,7 @@ use std::{
     ops::{Add, AddAssign},
     ptr,
 };
+use thin_vec::ThinVec;
 
 /// Compiled AST (abstract syntax tree) of a Rhai script.
 ///
@@ -22,7 +23,7 @@ pub struct AST {
     /// Source of the [`AST`].
     source: Option<ImmutableString>,
     /// Global statements.
-    body: Box<[Stmt]>,
+    body: ThinVec<Stmt>,
     /// Script-defined functions.
     #[cfg(not(feature = "no_function"))]
     lib: crate::SharedModule,
@@ -79,10 +80,7 @@ impl AST {
             source: None,
             #[cfg(feature = "metadata")]
             doc: crate::SmartString::new_const(),
-            body: statements
-                .into_iter()
-                .collect::<Vec<_>>()
-                .into_boxed_slice(),
+            body: statements.into_iter().collect(),
             #[cfg(not(feature = "no_function"))]
             lib: functions.into(),
             #[cfg(not(feature = "no_module"))]
@@ -102,10 +100,7 @@ impl AST {
             source: None,
             #[cfg(feature = "metadata")]
             doc: crate::SmartString::new_const(),
-            body: statements
-                .into_iter()
-                .collect::<Vec<_>>()
-                .into_boxed_slice(),
+            body: statements.into_iter().collect(),
             #[cfg(not(feature = "no_function"))]
             lib: functions.into(),
             #[cfg(not(feature = "no_module"))]
@@ -210,7 +205,7 @@ impl AST {
     #[cfg(not(feature = "internals"))]
     #[inline(always)]
     #[must_use]
-    pub(crate) const fn statements(&self) -> &[Stmt] {
+    pub(crate) fn statements(&self) -> &[Stmt] {
         &self.body
     }
     /// _(internals)_ Get the statements.
@@ -218,14 +213,14 @@ impl AST {
     #[cfg(feature = "internals")]
     #[inline(always)]
     #[must_use]
-    pub const fn statements(&self) -> &[Stmt] {
+    pub fn statements(&self) -> &[Stmt] {
         &self.body
     }
     /// Get the statements.
     #[inline(always)]
     #[must_use]
     #[allow(dead_code)]
-    pub(crate) fn statements_mut(&mut self) -> &mut Box<[Stmt]> {
+    pub(crate) fn statements_mut(&mut self) -> &mut ThinVec<Stmt> {
         &mut self.body
     }
     /// Does this [`AST`] contain script-defined functions?
@@ -643,12 +638,7 @@ impl AST {
         match (self.body.as_ref(), other.body.as_ref()) {
             (_, []) => (),
             ([], _) => self.body = other.body,
-            (_, _) => {
-                let mut body = self.body.to_vec();
-                let other = other.body.to_vec();
-                body.extend(other);
-                self.body = body.into_boxed_slice();
-            }
+            (_, _) => self.body.extend(other.body),
         }
 
         #[cfg(not(feature = "no_function"))]
@@ -711,7 +701,7 @@ impl AST {
     #[cfg(feature = "internals")]
     #[cfg(not(feature = "no_function"))]
     #[inline]
-    pub fn iter_fn_def(&self) -> impl Iterator<Item = &crate::Shared<super::ScriptFnDef>> {
+    pub fn iter_fn_def(&self) -> impl Iterator<Item = &crate::Shared<super::ScriptFuncDef>> {
         self.lib.iter_script_fn().map(|(.., fn_def)| fn_def)
     }
     /// Iterate through all function definitions.
@@ -721,7 +711,7 @@ impl AST {
     #[cfg(not(feature = "no_function"))]
     #[allow(dead_code)]
     #[inline]
-    pub(crate) fn iter_fn_def(&self) -> impl Iterator<Item = &crate::Shared<super::ScriptFnDef>> {
+    pub(crate) fn iter_fn_def(&self) -> impl Iterator<Item = &crate::Shared<super::ScriptFuncDef>> {
         self.lib.iter_script_fn().map(|(.., fn_def)| fn_def)
     }
     /// Iterate through all function definitions.
@@ -985,3 +975,23 @@ impl ASTNode<'_> {
         }
     }
 }
+
+/// _(internals)_ Encapsulated AST environment.
+/// Exported under the `internals` feature only.
+///
+/// 1) functions defined within the same AST
+/// 2) the stack of imported [modules][crate::Module]
+/// 3) global constants
+#[derive(Debug, Clone)]
+pub struct EncapsulatedEnviron {
+    /// Functions defined within the same [`AST`][crate::AST].
+    #[cfg(not(feature = "no_function"))]
+    pub lib: crate::SharedModule,
+    /// Imported [modules][crate::Module].
+    #[cfg(not(feature = "no_module"))]
+    pub imports: thin_vec::ThinVec<(ImmutableString, crate::SharedModule)>,
+    /// Globally-defined constants.
+    #[cfg(not(feature = "no_module"))]
+    #[cfg(not(feature = "no_function"))]
+    pub constants: Option<crate::eval::SharedGlobalConstants>,
+}
diff --git a/src/ast/expr.rs b/src/ast/expr.rs
index a1d121bbf..9964f0c83 100644
--- a/src/ast/expr.rs
+++ b/src/ast/expr.rs
@@ -5,8 +5,8 @@ use crate::engine::KEYWORD_FN_PTR;
 use crate::tokenizer::Token;
 use crate::types::dynamic::Union;
 use crate::{
-    calc_fn_hash, Dynamic, FnPtr, Identifier, ImmutableString, Position, SmartString, StaticVec,
-    INT,
+    calc_fn_hash, Dynamic, FnArgsVec, FnPtr, Identifier, ImmutableString, Position, SmartString,
+    StaticVec, INT,
 };
 #[cfg(feature = "no_std")]
 use std::prelude::v1::*;
@@ -23,7 +23,7 @@ use thin_vec::ThinVec;
 
 /// _(internals)_ A binary expression.
 /// Exported under the `internals` feature only.
-#[derive(Debug, Clone, Hash)]
+#[derive(Debug, Clone, Hash, Default)]
 pub struct BinaryExpr {
     /// LHS expression.
     pub lhs: Expr,
@@ -39,9 +39,9 @@ pub struct BinaryExpr {
 #[derive(Debug, Clone, Hash)]
 pub struct CustomExpr {
     /// List of keywords.
-    pub inputs: Box<[Expr]>,
+    pub inputs: FnArgsVec<Expr>,
     /// List of tokens actually parsed.
-    pub tokens: Box<[ImmutableString]>,
+    pub tokens: FnArgsVec<ImmutableString>,
     /// State value.
     pub state: Dynamic,
     /// Is the current [`Scope`][crate::Scope] possibly modified by this custom statement
@@ -191,7 +191,7 @@ pub struct FnCallExpr {
     /// Pre-calculated hashes.
     pub hashes: FnCallHashes,
     /// List of function call argument expressions.
-    pub args: Box<[Expr]>,
+    pub args: FnArgsVec<Expr>,
     /// Does this function call capture the parent scope?
     pub capture_parent_scope: bool,
     /// Is this function call a native operator?
diff --git a/src/ast/mod.rs b/src/ast/mod.rs
index 48808693f..69a63d244 100644
--- a/src/ast/mod.rs
+++ b/src/ast/mod.rs
@@ -10,7 +10,7 @@ pub mod namespace_none;
 pub mod script_fn;
 pub mod stmt;
 
-pub use ast::{ASTNode, AST};
+pub use ast::{ASTNode, EncapsulatedEnviron, AST};
 #[cfg(not(feature = "no_custom_syntax"))]
 pub use expr::CustomExpr;
 pub use expr::{BinaryExpr, Expr, FnCallExpr, FnCallHashes};
@@ -21,13 +21,13 @@ pub use namespace::Namespace;
 #[cfg(feature = "no_module")]
 pub use namespace_none::Namespace;
 #[cfg(not(feature = "no_function"))]
-pub use script_fn::{ScriptFnDef, ScriptFnMetadata};
+pub use script_fn::{ScriptFnMetadata, ScriptFuncDef};
 pub use stmt::{
-    CaseBlocksList, ConditionalExpr, FlowControl, OpAssignment, RangeCase, Stmt, StmtBlock,
-    StmtBlockContainer, SwitchCasesCollection,
+    CaseBlocksList, FlowControl, OpAssignment, RangeCase, Stmt, StmtBlock, StmtBlockContainer,
+    SwitchCasesCollection,
 };
 
 /// _(internals)_ Placeholder for a script-defined function.
 /// Exported under the `internals` feature only.
 #[cfg(feature = "no_function")]
-pub type ScriptFnDef = ();
+pub type ScriptFuncDef = ();
diff --git a/src/ast/script_fn.rs b/src/ast/script_fn.rs
index 74f892476..bd5b2dcde 100644
--- a/src/ast/script_fn.rs
+++ b/src/ast/script_fn.rs
@@ -10,7 +10,7 @@ use std::{fmt, hash::Hash};
 /// _(internals)_ A type containing information on a script-defined function.
 /// Exported under the `internals` feature only.
 #[derive(Debug, Clone)]
-pub struct ScriptFnDef {
+pub struct ScriptFuncDef {
     /// Function body.
     pub body: StmtBlock,
     /// Function name.
@@ -37,10 +37,10 @@ pub struct ScriptFnDef {
     ///
     /// Each line in non-block doc-comments starts with `///`.
     #[cfg(feature = "metadata")]
-    pub comments: Box<[crate::SmartString]>,
+    pub comments: crate::StaticVec<crate::SmartString>,
 }
 
-impl fmt::Display for ScriptFnDef {
+impl fmt::Display for ScriptFuncDef {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         #[cfg(not(feature = "no_object"))]
         let this_type = self
@@ -148,9 +148,9 @@ impl fmt::Display for ScriptFnMetadata<'_> {
     }
 }
 
-impl<'a> From<&'a ScriptFnDef> for ScriptFnMetadata<'a> {
+impl<'a> From<&'a ScriptFuncDef> for ScriptFnMetadata<'a> {
     #[inline]
-    fn from(value: &'a ScriptFnDef) -> Self {
+    fn from(value: &'a ScriptFuncDef) -> Self {
         Self {
             name: &value.name,
             params: value.params.iter().map(ImmutableString::as_str).collect(),
diff --git a/src/ast/stmt.rs b/src/ast/stmt.rs
index 358fe5554..c9eff5aa1 100644
--- a/src/ast/stmt.rs
+++ b/src/ast/stmt.rs
@@ -6,7 +6,7 @@ use crate::func::StraightHashMap;
 use crate::tokenizer::Token;
 use crate::types::dynamic::Union;
 use crate::types::Span;
-use crate::{calc_fn_hash, Dynamic, Position, INT};
+use crate::{calc_fn_hash, Dynamic, FnArgsVec, Position, StaticVec, INT};
 #[cfg(feature = "no_std")]
 use std::prelude::v1::*;
 use std::{
@@ -17,7 +17,6 @@ use std::{
     num::NonZeroUsize,
     ops::{Range, RangeInclusive},
 };
-use thin_vec::ThinVec;
 
 /// _(internals)_ An op-assignment operator.
 /// Exported under the `internals` feature only.
@@ -180,53 +179,6 @@ impl fmt::Debug for OpAssignment {
     }
 }
 
-/// _(internals)_ An expression with a condition.
-/// Exported under the `internals` feature only.
-///
-/// The condition may simply be [`Expr::BoolConstant`] with `true` if there is actually no condition.
-#[derive(Debug, Clone, Default, Hash)]
-pub struct ConditionalExpr {
-    /// Condition.
-    pub condition: Expr,
-    /// Expression.
-    pub expr: Expr,
-}
-
-impl<E: Into<Expr>> From<E> for ConditionalExpr {
-    #[inline(always)]
-    fn from(value: E) -> Self {
-        Self {
-            condition: Expr::BoolConstant(true, Position::NONE),
-            expr: value.into(),
-        }
-    }
-}
-
-impl<E: Into<Expr>> From<(Expr, E)> for ConditionalExpr {
-    #[inline(always)]
-    fn from(value: (Expr, E)) -> Self {
-        Self {
-            condition: value.0,
-            expr: value.1.into(),
-        }
-    }
-}
-
-impl ConditionalExpr {
-    /// Is the condition always `true`?
-    #[inline(always)]
-    #[must_use]
-    pub const fn is_always_true(&self) -> bool {
-        matches!(self.condition, Expr::BoolConstant(true, ..))
-    }
-    /// Is the condition always `false`?
-    #[inline(always)]
-    #[must_use]
-    pub const fn is_always_false(&self) -> bool {
-        matches!(self.condition, Expr::BoolConstant(false, ..))
-    }
-}
-
 /// _(internals)_ A type containing a range case for a `switch` statement.
 /// Exported under the `internals` feature only.
 #[derive(Clone, Hash)]
@@ -379,12 +331,12 @@ pub type CaseBlocksList = smallvec::SmallVec<[usize; 2]>;
 /// Exported under the `internals` feature only.
 #[derive(Debug, Clone)]
 pub struct SwitchCasesCollection {
-    /// List of [`ConditionalExpr`]'s.
-    pub expressions: ThinVec<ConditionalExpr>,
+    /// List of conditional expressions: LHS = condition, RHS = expression.
+    pub expressions: FnArgsVec<BinaryExpr>,
     /// Dictionary mapping value hashes to [`ConditionalExpr`]'s.
     pub cases: StraightHashMap<CaseBlocksList>,
     /// List of range cases.
-    pub ranges: ThinVec<RangeCase>,
+    pub ranges: StaticVec<RangeCase>,
     /// Statements block for the default case (there can be no condition for the default case).
     pub def_case: Option<usize>,
 }
@@ -902,14 +854,14 @@ impl Stmt {
                 expr.is_pure()
                     && sw.cases.values().flat_map(|cases| cases.iter()).all(|&c| {
                         let block = &sw.expressions[c];
-                        block.condition.is_pure() && block.expr.is_pure()
+                        block.lhs.is_pure() && block.rhs.is_pure()
                     })
                     && sw.ranges.iter().all(|r| {
                         let block = &sw.expressions[r.index()];
-                        block.condition.is_pure() && block.expr.is_pure()
+                        block.lhs.is_pure() && block.rhs.is_pure()
                     })
                     && sw.def_case.is_some()
-                    && sw.expressions[sw.def_case.unwrap()].expr.is_pure()
+                    && sw.expressions[sw.def_case.unwrap()].rhs.is_pure()
             }
 
             // Loops that exit can be pure because it can never be infinite.
@@ -1059,10 +1011,10 @@ impl Stmt {
                     for &b in blocks {
                         let block = &sw.expressions[b];
 
-                        if !block.condition.walk(path, on_node) {
+                        if !block.lhs.walk(path, on_node) {
                             return false;
                         }
-                        if !block.expr.walk(path, on_node) {
+                        if !block.rhs.walk(path, on_node) {
                             return false;
                         }
                     }
@@ -1070,15 +1022,15 @@ impl Stmt {
                 for r in &sw.ranges {
                     let block = &sw.expressions[r.index()];
 
-                    if !block.condition.walk(path, on_node) {
+                    if !block.lhs.walk(path, on_node) {
                         return false;
                     }
-                    if !block.expr.walk(path, on_node) {
+                    if !block.rhs.walk(path, on_node) {
                         return false;
                     }
                 }
                 if let Some(index) = sw.def_case {
-                    if !sw.expressions[index].expr.walk(path, on_node) {
+                    if !sw.expressions[index].lhs.walk(path, on_node) {
                         return false;
                     }
                 }
diff --git a/src/engine.rs b/src/engine.rs
index 91278e2e7..d974d4aec 100644
--- a/src/engine.rs
+++ b/src/engine.rs
@@ -314,25 +314,11 @@ impl Engine {
     }
 
     /// Get an interned [string][ImmutableString].
-    #[cfg(not(feature = "internals"))]
-    #[inline(always)]
-    #[must_use]
-    pub(crate) fn get_interned_string(
-        &self,
-        string: impl AsRef<str> + Into<ImmutableString>,
-    ) -> ImmutableString {
-        match self.interned_strings {
-            Some(ref interner) => locked_write(interner).get(string),
-            _ => string.into(),
-        }
-    }
-
-    /// _(internals)_ Get an interned [string][ImmutableString].
-    /// Exported under the `internals` feature only.
     ///
     /// [`Engine`] keeps a cache of [`ImmutableString`] instances and tries to avoid new allocations
-    /// when an existing instance is found.
-    #[cfg(feature = "internals")]
+    /// and save memory when an existing instance is found.
+    ///
+    /// It is usually a good idea to intern strings if they are used frequently.
     #[inline]
     #[must_use]
     pub fn get_interned_string(
diff --git a/src/eval/cache.rs b/src/eval/cache.rs
index 25302de4a..8feedb05a 100644
--- a/src/eval/cache.rs
+++ b/src/eval/cache.rs
@@ -1,6 +1,6 @@
 //! System caches.
 
-use crate::func::{CallableFunction, StraightHashMap};
+use crate::func::{RhaiFunc, StraightHashMap};
 use crate::types::BloomFilterU64;
 use crate::{ImmutableString, StaticVec};
 #[cfg(feature = "no_std")]
@@ -11,7 +11,7 @@ use std::prelude::v1::*;
 #[derive(Debug, Clone)]
 pub struct FnResolutionCacheEntry {
     /// Function.
-    pub func: CallableFunction,
+    pub func: RhaiFunc,
     /// Optional source.
     pub source: Option<ImmutableString>,
 }
diff --git a/src/eval/debugger.rs b/src/eval/debugger.rs
index fb2a576eb..f6c6e7ba4 100644
--- a/src/eval/debugger.rs
+++ b/src/eval/debugger.rs
@@ -253,7 +253,7 @@ pub struct Debugger {
     /// The current set of break-points.
     break_points: Vec<BreakPoint>,
     /// The current function call stack.
-    call_stack: ThinVec<CallStackFrame>,
+    call_stack: Vec<CallStackFrame>,
     /// The current state.
     state: Dynamic,
 }
@@ -266,7 +266,7 @@ impl Debugger {
         Self {
             status,
             break_points: Vec::new(),
-            call_stack: ThinVec::new(),
+            call_stack: Vec::new(),
             state: Dynamic::UNIT,
         }
     }
diff --git a/src/eval/expr.rs b/src/eval/expr.rs
index dcb175cf4..9e9468f3b 100644
--- a/src/eval/expr.rs
+++ b/src/eval/expr.rs
@@ -73,7 +73,7 @@ pub fn search_scope_only<'s>(
             {
                 let val: Dynamic = crate::FnPtr {
                     name: v.3.clone(),
-                    curry: thin_vec::ThinVec::new(),
+                    curry: <_>::default(),
                     environ: None,
                     fn_def: Some(fn_def.clone()),
                 }
diff --git a/src/eval/global_state.rs b/src/eval/global_state.rs
index 501348e6b..3990d84cb 100644
--- a/src/eval/global_state.rs
+++ b/src/eval/global_state.rs
@@ -224,7 +224,7 @@ impl GlobalRuntimeState {
         &self,
         hash: u64,
         global_namespace_only: bool,
-    ) -> Option<(&crate::func::CallableFunction, Option<&ImmutableString>)> {
+    ) -> Option<(&crate::func::RhaiFunc, Option<&ImmutableString>)> {
         if global_namespace_only {
             self.modules
                 .iter()
@@ -256,7 +256,7 @@ impl GlobalRuntimeState {
     #[cfg(not(feature = "no_module"))]
     #[inline]
     #[must_use]
-    pub fn get_iter(&self, id: std::any::TypeId) -> Option<&crate::func::IteratorFn> {
+    pub fn get_iter(&self, id: std::any::TypeId) -> Option<&crate::func::FnIterator> {
         self.modules
             .iter()
             .rev()
diff --git a/src/eval/mod.rs b/src/eval/mod.rs
index 476301b38..de82c5200 100644
--- a/src/eval/mod.rs
+++ b/src/eval/mod.rs
@@ -15,11 +15,15 @@ pub use cache::{Caches, FnResolutionCacheEntry};
 #[cfg(not(feature = "no_index"))]
 pub use data_check::calc_array_sizes;
 #[cfg(not(feature = "unchecked"))]
+#[cfg(any(not(feature = "no_index"), not(feature = "no_object")))]
 pub use data_check::calc_data_sizes;
 #[cfg(feature = "debugging")]
+#[cfg(not(feature = "no_function"))]
+pub use debugger::CallStackFrame;
+#[cfg(feature = "debugging")]
 pub use debugger::{
-    BreakPoint, CallStackFrame, Debugger, DebuggerCommand, DebuggerEvent, DebuggerStatus,
-    OnDebuggerCallback, OnDebuggingInit,
+    BreakPoint, Debugger, DebuggerCommand, DebuggerEvent, DebuggerStatus, OnDebuggerCallback,
+    OnDebuggingInit,
 };
 pub use eval_context::EvalContext;
 #[cfg(not(feature = "no_module"))]
diff --git a/src/eval/stmt.rs b/src/eval/stmt.rs
index 540aaf5df..ca2e06798 100644
--- a/src/eval/stmt.rs
+++ b/src/eval/stmt.rs
@@ -2,8 +2,7 @@
 
 use super::{Caches, EvalContext, GlobalRuntimeState, Target};
 use crate::ast::{
-    ASTFlags, BinaryExpr, ConditionalExpr, Expr, FlowControl, OpAssignment, Stmt,
-    SwitchCasesCollection,
+    ASTFlags, BinaryExpr, Expr, FlowControl, OpAssignment, Stmt, SwitchCasesCollection,
 };
 use crate::eval::search_namespace;
 use crate::func::{get_builtin_op_assignment_fn, get_hasher};
@@ -526,7 +525,7 @@ impl Engine {
                         for &index in case_blocks_list {
                             let block = &expressions[index];
 
-                            let cond_result = match block.condition {
+                            let cond_result = match block.lhs {
                                 Expr::BoolConstant(b, ..) => b,
                                 ref c => self
                                     .eval_expr(global, caches, scope, this_ptr.as_deref_mut(), c)?
@@ -537,16 +536,16 @@ impl Engine {
                             };
 
                             if cond_result {
-                                result = Some(&block.expr);
+                                result = Some(&block.rhs);
                                 break;
                             }
                         }
                     } else if !ranges.is_empty() {
                         // Then check integer ranges
                         for r in ranges.iter().filter(|r| r.contains(&value)) {
-                            let ConditionalExpr { condition, expr } = &expressions[r.index()];
+                            let BinaryExpr { lhs, rhs } = &expressions[r.index()];
 
-                            let cond_result = match condition {
+                            let cond_result = match lhs {
                                 Expr::BoolConstant(b, ..) => *b,
                                 c => self
                                     .eval_expr(global, caches, scope, this_ptr.as_deref_mut(), c)?
@@ -557,7 +556,7 @@ impl Engine {
                             };
 
                             if cond_result {
-                                result = Some(expr);
+                                result = Some(rhs);
                                 break;
                             }
                         }
@@ -565,7 +564,7 @@ impl Engine {
                 }
 
                 result
-                    .or_else(|| def_case.as_ref().map(|&index| &expressions[index].expr))
+                    .or_else(|| def_case.as_ref().map(|&index| &expressions[index].rhs))
                     .map_or(Ok(Dynamic::UNIT), |expr| {
                         self.eval_expr(global, caches, scope, this_ptr, expr)
                     })
diff --git a/src/func/call.rs b/src/func/call.rs
index baa7a0ad0..1980e8096 100644
--- a/src/func/call.rs
+++ b/src/func/call.rs
@@ -1,6 +1,6 @@
 //! Implement function-calling mechanism for [`Engine`].
 
-use super::{get_builtin_binary_op_fn, get_builtin_op_assignment_fn, CallableFunction};
+use super::{get_builtin_binary_op_fn, get_builtin_op_assignment_fn, RhaiFunc};
 use crate::api::default_limits::MAX_DYNAMIC_PARAMETERS;
 use crate::ast::{Expr, FnCallExpr, FnCallHashes};
 use crate::engine::{
@@ -277,7 +277,7 @@ impl Engine {
 
                                     get_builtin_op_assignment_fn(token, first_arg, rest_args[0])
                                         .map(|(f, has_context)| FnResolutionCacheEntry {
-                                            func: CallableFunction::Method {
+                                            func: RhaiFunc::Method {
                                                 func: Shared::new(f),
                                                 has_context,
                                                 is_pure: false,
@@ -288,7 +288,7 @@ impl Engine {
                                 }
                                 Some(token) => get_builtin_binary_op_fn(token, args[0], args[1])
                                     .map(|(f, has_context)| FnResolutionCacheEntry {
-                                        func: CallableFunction::Method {
+                                        func: RhaiFunc::Method {
                                             func: Shared::new(f),
                                             has_context,
                                             is_pure: true,
@@ -407,10 +407,8 @@ impl Engine {
                 f if !f.is_pure() && !args.is_empty() && args[0].is_read_only() => {
                     Err(ERR::ErrorNonPureMethodCallOnConstant(name.to_string(), pos).into())
                 }
-                CallableFunction::Plugin { func } => func.call(context, args),
-                CallableFunction::Pure { func, .. } | CallableFunction::Method { func, .. } => {
-                    func(context, args)
-                }
+                RhaiFunc::Plugin { func } => func.call(context, args),
+                RhaiFunc::Pure { func, .. } | RhaiFunc::Method { func, .. } => func(context, args),
                 _ => unreachable!("non-native function"),
             }
             .and_then(|r| self.check_data_size(r, pos))
@@ -628,7 +626,7 @@ impl Engine {
             }
 
             if let Some(FnResolutionCacheEntry { func, source }) = resolved.cloned() {
-                let CallableFunction::Script { fn_def, environ } = func else {
+                let RhaiFunc::Script { fn_def, environ } = func else {
                     unreachable!("Script function expected");
                 };
 
@@ -1529,7 +1527,7 @@ impl Engine {
         }
 
         // Clone first argument if the function is not a method after-all
-        if !func.map_or(true, CallableFunction::is_method) {
+        if !func.map_or(true, RhaiFunc::is_method) {
             if let Some(first) = first_arg_value {
                 *first = args[0].clone();
                 args[0] = first;
@@ -1540,7 +1538,7 @@ impl Engine {
 
         match func {
             #[cfg(not(feature = "no_function"))]
-            Some(CallableFunction::Script { fn_def, environ }) => {
+            Some(RhaiFunc::Script { fn_def, environ }) => {
                 let environ = environ.as_deref();
                 let scope = &mut Scope::new();
 
@@ -1557,7 +1555,7 @@ impl Engine {
                 Err(ERR::ErrorNonPureMethodCallOnConstant(fn_name.to_string(), pos).into())
             }
 
-            Some(CallableFunction::Plugin { func }) => {
+            Some(RhaiFunc::Plugin { func }) => {
                 let context = func
                     .has_context()
                     .then(|| (self, fn_name, module.id(), &*global, pos).into());
@@ -1566,10 +1564,10 @@ impl Engine {
             }
 
             Some(
-                CallableFunction::Pure {
+                RhaiFunc::Pure {
                     func, has_context, ..
                 }
-                | CallableFunction::Method {
+                | RhaiFunc::Method {
                     func, has_context, ..
                 },
             ) => {
@@ -1578,7 +1576,7 @@ impl Engine {
                 func(context, args).and_then(|r| self.check_data_size(r, pos))
             }
 
-            Some(CallableFunction::Iterator { .. }) => {
+            Some(RhaiFunc::Iterator { .. }) => {
                 unreachable!("iterator functions should not occur here")
             }
 
diff --git a/src/func/args.rs b/src/func/func_args.rs
similarity index 100%
rename from src/func/args.rs
rename to src/func/func_args.rs
diff --git a/src/func/func.rs b/src/func/func_trait.rs
similarity index 100%
rename from src/func/func.rs
rename to src/func/func_trait.rs
diff --git a/src/func/callable_function.rs b/src/func/function.rs
similarity index 85%
rename from src/func/callable_function.rs
rename to src/func/function.rs
index 61412348f..5587b9480 100644
--- a/src/func/callable_function.rs
+++ b/src/func/function.rs
@@ -1,38 +1,18 @@
 //! Module defining the standard Rhai function type.
 
-use super::native::{FnAny, FnPlugin, IteratorFn, SendSync};
-use crate::ast::FnAccess;
-use crate::plugin::PluginFunction;
+use super::native::{FnAny, FnIterator, FnPlugin, SendSync};
+use crate::ast::{EncapsulatedEnviron, FnAccess};
+use crate::plugin::PluginFunc;
 use crate::Shared;
 use std::fmt;
 #[cfg(feature = "no_std")]
 use std::prelude::v1::*;
 
-/// _(internals)_ Encapsulated AST environment.
-/// Exported under the `internals` feature only.
-///
-/// 1) functions defined within the same AST
-/// 2) the stack of imported [modules][crate::Module]
-/// 3) global constants
-#[derive(Debug, Clone)]
-pub struct EncapsulatedEnviron {
-    /// Functions defined within the same [`AST`][crate::AST].
-    #[cfg(not(feature = "no_function"))]
-    pub lib: crate::SharedModule,
-    /// Imported [modules][crate::Module].
-    #[cfg(not(feature = "no_module"))]
-    pub imports: thin_vec::ThinVec<(crate::ImmutableString, crate::SharedModule)>,
-    /// Globally-defined constants.
-    #[cfg(not(feature = "no_module"))]
-    #[cfg(not(feature = "no_function"))]
-    pub constants: Option<crate::eval::SharedGlobalConstants>,
-}
-
 /// _(internals)_ A type encapsulating a function callable by Rhai.
 /// Exported under the `internals` feature only.
 #[derive(Clone)]
 #[non_exhaustive]
-pub enum CallableFunction {
+pub enum RhaiFunc {
     /// A pure native Rust function with all arguments passed by value.
     Pure {
         /// Shared function pointer.
@@ -63,7 +43,7 @@ pub enum CallableFunction {
     /// An iterator function.
     Iterator {
         /// Shared function pointer.
-        func: Shared<IteratorFn>,
+        func: Shared<FnIterator>,
     },
     /// A plugin function,
     Plugin {
@@ -73,14 +53,14 @@ pub enum CallableFunction {
     /// A script-defined function.
     #[cfg(not(feature = "no_function"))]
     Script {
-        /// Shared reference to the [`ScriptFnDef`][crate::ast::ScriptFnDef] function definition.
-        fn_def: Shared<crate::ast::ScriptFnDef>,
+        /// Shared reference to the [`ScriptFuncDef`][crate::ast::ScriptFuncDef] function definition.
+        fn_def: Shared<crate::ast::ScriptFuncDef>,
         /// Encapsulated environment, if any.
         environ: Option<Shared<EncapsulatedEnviron>>,
     },
 }
 
-impl fmt::Debug for CallableFunction {
+impl fmt::Debug for RhaiFunc {
     #[cold]
     #[inline(never)]
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
@@ -96,7 +76,7 @@ impl fmt::Debug for CallableFunction {
     }
 }
 
-impl fmt::Display for CallableFunction {
+impl fmt::Display for RhaiFunc {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self {
             Self::Pure { .. } => f.write_str("NativePureFunction"),
@@ -110,7 +90,7 @@ impl fmt::Display for CallableFunction {
     }
 }
 
-impl CallableFunction {
+impl RhaiFunc {
     /// Is this a pure native Rust function?
     #[inline]
     #[must_use]
@@ -260,7 +240,7 @@ impl CallableFunction {
     #[cfg(not(feature = "no_function"))]
     #[inline]
     #[must_use]
-    pub const fn get_script_fn_def(&self) -> Option<&Shared<crate::ast::ScriptFnDef>> {
+    pub const fn get_script_fn_def(&self) -> Option<&Shared<crate::ast::ScriptFuncDef>> {
         match self {
             Self::Pure { .. }
             | Self::Method { .. }
@@ -288,7 +268,7 @@ impl CallableFunction {
     /// Get a reference to an iterator function.
     #[inline]
     #[must_use]
-    pub fn get_iter_fn(&self) -> Option<&IteratorFn> {
+    pub fn get_iter_fn(&self) -> Option<&FnIterator> {
         match self {
             Self::Iterator { func, .. } => Some(&**func),
             Self::Pure { .. } | Self::Method { .. } | Self::Plugin { .. } => None,
@@ -312,9 +292,9 @@ impl CallableFunction {
 }
 
 #[cfg(not(feature = "no_function"))]
-impl From<crate::ast::ScriptFnDef> for CallableFunction {
+impl From<crate::ast::ScriptFuncDef> for RhaiFunc {
     #[inline(always)]
-    fn from(fn_def: crate::ast::ScriptFnDef) -> Self {
+    fn from(fn_def: crate::ast::ScriptFuncDef) -> Self {
         Self::Script {
             fn_def: fn_def.into(),
             environ: None,
@@ -323,9 +303,9 @@ impl From<crate::ast::ScriptFnDef> for CallableFunction {
 }
 
 #[cfg(not(feature = "no_function"))]
-impl From<Shared<crate::ast::ScriptFnDef>> for CallableFunction {
+impl From<Shared<crate::ast::ScriptFuncDef>> for RhaiFunc {
     #[inline(always)]
-    fn from(fn_def: Shared<crate::ast::ScriptFnDef>) -> Self {
+    fn from(fn_def: Shared<crate::ast::ScriptFuncDef>) -> Self {
         Self::Script {
             fn_def,
             environ: None,
@@ -333,7 +313,7 @@ impl From<Shared<crate::ast::ScriptFnDef>> for CallableFunction {
     }
 }
 
-impl<T: PluginFunction + 'static + SendSync> From<T> for CallableFunction {
+impl<T: PluginFunc + 'static + SendSync> From<T> for RhaiFunc {
     #[inline(always)]
     fn from(func: T) -> Self {
         Self::Plugin {
@@ -342,7 +322,7 @@ impl<T: PluginFunction + 'static + SendSync> From<T> for CallableFunction {
     }
 }
 
-impl From<Shared<FnPlugin>> for CallableFunction {
+impl From<Shared<FnPlugin>> for RhaiFunc {
     #[inline(always)]
     fn from(func: Shared<FnPlugin>) -> Self {
         Self::Plugin { func }
diff --git a/src/func/mod.rs b/src/func/mod.rs
index 61471a53f..f8ed25dd0 100644
--- a/src/func/mod.rs
+++ b/src/func/mod.rs
@@ -1,27 +1,27 @@
 //! Module defining mechanisms to handle function calls in Rhai.
 
-pub mod args;
 pub mod builtin;
 pub mod call;
-pub mod callable_function;
+pub mod func_args;
 #[allow(clippy::module_inception)]
-pub mod func;
+pub mod func_trait;
+pub mod function;
 pub mod hashing;
 pub mod native;
 pub mod plugin;
 pub mod register;
 pub mod script;
 
-pub use args::FuncArgs;
 pub use builtin::{get_builtin_binary_op_fn, get_builtin_op_assignment_fn};
 #[cfg(not(feature = "no_closure"))]
 pub use call::ensure_no_data_race;
 #[cfg(not(feature = "no_function"))]
 pub use call::is_anonymous_fn;
 pub use call::FnCallArgs;
-pub use callable_function::{CallableFunction, EncapsulatedEnviron};
+pub use func_args::FuncArgs;
 #[cfg(not(feature = "no_function"))]
-pub use func::Func;
+pub use func_trait::Func;
+pub use function::RhaiFunc;
 #[cfg(not(feature = "no_object"))]
 #[cfg(not(feature = "no_function"))]
 pub use hashing::calc_typed_method_hash;
@@ -29,8 +29,9 @@ pub use hashing::{calc_fn_hash, calc_fn_hash_full, calc_var_hash, get_hasher, St
 #[cfg(feature = "internals")]
 #[allow(deprecated)]
 pub use native::NativeCallContextStore;
+#[allow(unused_imports)]
 pub use native::{
     locked_read, locked_write, shared_get_mut, shared_make_mut, shared_take, shared_take_or_clone,
-    shared_try_take, IteratorFn, Locked, NativeCallContext, SendSync, Shared,
+    FnIterator, Locked, NativeCallContext, SendSync, Shared,
 };
-pub use register::RegisterNativeFunction;
+pub use register::RhaiNativeFunc;
diff --git a/src/func/native.rs b/src/func/native.rs
index 4548773b5..f527537f3 100644
--- a/src/func/native.rs
+++ b/src/func/native.rs
@@ -3,7 +3,7 @@
 use super::call::FnCallArgs;
 use crate::ast::FnCallHashes;
 use crate::eval::{Caches, GlobalRuntimeState};
-use crate::plugin::PluginFunction;
+use crate::plugin::PluginFunc;
 use crate::tokenizer::{is_valid_function_name, Token, TokenizeState};
 use crate::types::dynamic::Variant;
 use crate::{
@@ -568,18 +568,18 @@ pub type FnBuiltin = (
 
 /// Function that gets an iterator from a type.
 #[cfg(not(feature = "sync"))]
-pub type IteratorFn = dyn Fn(Dynamic) -> Box<dyn Iterator<Item = RhaiResultOf<Dynamic>>>;
+pub type FnIterator = dyn Fn(Dynamic) -> Box<dyn Iterator<Item = RhaiResultOf<Dynamic>>>;
 /// Function that gets an iterator from a type.
 #[cfg(feature = "sync")]
-pub type IteratorFn =
+pub type FnIterator =
     dyn Fn(Dynamic) -> Box<dyn Iterator<Item = RhaiResultOf<Dynamic>>> + Send + Sync;
 
 /// Plugin function trait object.
 #[cfg(not(feature = "sync"))]
-pub type FnPlugin = dyn PluginFunction;
+pub type FnPlugin = dyn PluginFunc;
 /// Plugin function trait object.
 #[cfg(feature = "sync")]
-pub type FnPlugin = dyn PluginFunction + Send + Sync;
+pub type FnPlugin = dyn PluginFunc + Send + Sync;
 
 /// Callback function for progress reporting.
 #[cfg(not(feature = "unchecked"))]
diff --git a/src/func/plugin.rs b/src/func/plugin.rs
index 2c8427718..9ca1889cd 100644
--- a/src/func/plugin.rs
+++ b/src/func/plugin.rs
@@ -1,10 +1,10 @@
 //! Module defining macros for developing _plugins_.
 
-pub use super::CallableFunction;
 use super::FnCallArgs;
+pub use super::RhaiFunc;
 pub use crate::{
-    Dynamic, Engine, EvalAltResult, FnAccess, FnNamespace, ImmutableString, Module,
-    NativeCallContext, Position,
+    Dynamic, Engine, EvalAltResult, FnAccess, FnNamespace, FuncRegistration, ImmutableString,
+    Module, NativeCallContext, Position,
 };
 #[cfg(feature = "no_std")]
 use std::prelude::v1::*;
@@ -20,7 +20,7 @@ pub use rhai_codegen::*;
 ///
 /// This trait should not be used directly.
 /// Use the `#[export_module]` and `#[export_fn]` procedural attributes instead.
-pub trait PluginFunction {
+pub trait PluginFunc {
     /// Call the plugin function with the arguments provided.
     fn call(&self, context: Option<NativeCallContext>, args: &mut FnCallArgs) -> RhaiResult;
 
diff --git a/src/func/register.rs b/src/func/register.rs
index 41c53f417..7f6024059 100644
--- a/src/func/register.rs
+++ b/src/func/register.rs
@@ -6,7 +6,7 @@
 #![allow(unused_variables)]
 
 use super::call::FnCallArgs;
-use super::callable_function::CallableFunction;
+use super::function::RhaiFunc;
 use super::native::{SendSync, Shared};
 use crate::types::dynamic::{DynamicWriteLock, Union, Variant};
 use crate::{Dynamic, Identifier, NativeCallContext, RhaiResultOf};
@@ -25,13 +25,13 @@ use std::{
 ///
 /// # Examples
 ///
-/// `RegisterNativeFunction<(Mut<A>, B, Ref<C>), 3, false, R, false>` = `Fn(&mut A, B, &C) -> R`
+/// `RhaiNativeFunc<(Mut<A>, B, Ref<C>), 3, false, R, false>` = `Fn(&mut A, B, &C) -> R`
 ///
-/// `RegisterNativeFunction<(Mut<A>, B, Ref<C>), 3, true,  R, false>` = `Fn(NativeCallContext, &mut A, B, &C) -> R`
+/// `RhaiNativeFunc<(Mut<A>, B, Ref<C>), 3, true,  R, false>` = `Fn(NativeCallContext, &mut A, B, &C) -> R`
 ///
-/// `RegisterNativeFunction<(Mut<A>, B, Ref<C>), 3, false, R, true>`  = `Fn(&mut A, B, &C) -> Result<R, Box<EvalAltResult>>`
+/// `RhaiNativeFunc<(Mut<A>, B, Ref<C>), 3, false, R, true>`  = `Fn(&mut A, B, &C) -> Result<R, Box<EvalAltResult>>`
 ///
-/// `RegisterNativeFunction<(Mut<A>, B, Ref<C>), 3, true,  R, true>`  = `Fn(NativeCallContext, &mut A, B, &C) -> Result<R, Box<EvalAltResult>>`
+/// `RhaiNativeFunc<(Mut<A>, B, Ref<C>), 3, true,  R, true>`  = `Fn(NativeCallContext, &mut A, B, &C) -> Result<R, Box<EvalAltResult>>`
 ///
 /// These types are not actually used anywhere.
 pub struct Mut<T>(T);
@@ -78,22 +78,10 @@ pub fn by_value<T: Variant + Clone>(data: &mut Dynamic) -> T {
 /// * `X` - a constant boolean generic indicating whether there is a `NativeCallContext` parameter.
 /// * `R` - return type of the function; if the function returns `Result`, it is the unwrapped inner value type.
 /// * `F` - a constant boolean generic indicating whether the function is fallible (i.e. returns `Result<T, Box<EvalAltResult>>`).
-pub trait RegisterNativeFunction<
-    A: 'static,
-    const N: usize,
-    const X: bool,
-    R: 'static,
-    const F: bool,
->
-{
-    /// Convert this function into a [`CallableFunction`].
+pub trait RhaiNativeFunc<A: 'static, const N: usize, const X: bool, R: 'static, const F: bool> {
+    /// Convert this function into a [`RhaiFunc`].
     #[must_use]
-    fn into_callable_function(
-        self,
-        name: Identifier,
-        is_pure: bool,
-        is_volatile: bool,
-    ) -> CallableFunction;
+    fn into_callable_function(self, is_pure: bool, is_volatile: bool) -> RhaiFunc;
     /// Get the type ID's of this function's parameters.
     #[must_use]
     fn param_types() -> [TypeId; N];
@@ -153,11 +141,11 @@ macro_rules! def_register {
             FN: Fn($($param),*) -> RET + SendSync + 'static,
             $($par: Variant + Clone,)*
             RET: Variant + Clone,
-        > RegisterNativeFunction<($($mark,)*), $n, false, RET, false> for FN {
+        > RhaiNativeFunc<($($mark,)*), $n, false, RET, false> for FN {
             #[inline(always)] fn param_types() -> [TypeId;$n] { [$(TypeId::of::<$par>()),*] }
             #[cfg(feature = "metadata")] #[inline(always)] fn param_names() -> [&'static str;$n] { [$(type_name::<$param>()),*] }
-            #[inline(always)] fn into_callable_function(self, fn_name: Identifier, is_pure: bool, is_volatile: bool) -> CallableFunction {
-                CallableFunction::$abi { func: Shared::new(move |_, args: &mut FnCallArgs| {
+            #[inline(always)] fn into_callable_function(self, is_pure: bool, is_volatile: bool) -> RhaiFunc {
+                RhaiFunc::$abi { func: Shared::new(move |_, args: &mut FnCallArgs| {
                     // The arguments are assumed to be of the correct number and types!
                     let mut drain = args.iter_mut();
                     $(let mut $par = $clone(drain.next().unwrap()); )*
@@ -175,11 +163,11 @@ macro_rules! def_register {
             FN: for<'a> Fn(NativeCallContext<'a>, $($param),*) -> RET + SendSync + 'static,
             $($par: Variant + Clone,)*
             RET: Variant + Clone,
-        > RegisterNativeFunction<($($mark,)*), $n, true, RET, false> for FN {
+        > RhaiNativeFunc<($($mark,)*), $n, true, RET, false> for FN {
             #[inline(always)] fn param_types() -> [TypeId;$n] { [$(TypeId::of::<$par>()),*] }
             #[cfg(feature = "metadata")] #[inline(always)] fn param_names() -> [&'static str;$n] { [$(type_name::<$param>()),*] }
-            #[inline(always)] fn into_callable_function(self, fn_name: Identifier, is_pure: bool, is_volatile: bool) -> CallableFunction {
-                CallableFunction::$abi { func: Shared::new(move |ctx: Option<NativeCallContext>, args: &mut FnCallArgs| {
+            #[inline(always)] fn into_callable_function(self, is_pure: bool, is_volatile: bool) -> RhaiFunc {
+                RhaiFunc::$abi { func: Shared::new(move |ctx: Option<NativeCallContext>, args: &mut FnCallArgs| {
                     let ctx = ctx.unwrap();
 
                     // The arguments are assumed to be of the correct number and types!
@@ -199,12 +187,12 @@ macro_rules! def_register {
             FN: Fn($($param),*) -> RhaiResultOf<RET> + SendSync + 'static,
             $($par: Variant + Clone,)*
             RET: Variant + Clone
-        > RegisterNativeFunction<($($mark,)*), $n, false, RET, true> for FN {
+        > RhaiNativeFunc<($($mark,)*), $n, false, RET, true> for FN {
             #[inline(always)] fn param_types() -> [TypeId;$n] { [$(TypeId::of::<$par>()),*] }
             #[cfg(feature = "metadata")] #[inline(always)] fn param_names() -> [&'static str;$n] { [$(type_name::<$param>()),*] }
             #[cfg(feature = "metadata")] #[inline(always)] fn return_type_name() -> &'static str { type_name::<RhaiResultOf<RET>>() }
-            #[inline(always)] fn into_callable_function(self, fn_name: Identifier, is_pure: bool, is_volatile: bool) -> CallableFunction {
-                CallableFunction::$abi { func: Shared::new(move |_, args: &mut FnCallArgs| {
+            #[inline(always)] fn into_callable_function(self, is_pure: bool, is_volatile: bool) -> RhaiFunc {
+                RhaiFunc::$abi { func: Shared::new(move |_, args: &mut FnCallArgs| {
                     // The arguments are assumed to be of the correct number and types!
                     let mut drain = args.iter_mut();
                     $(let mut $par = $clone(drain.next().unwrap()); )*
@@ -219,12 +207,12 @@ macro_rules! def_register {
             FN: for<'a> Fn(NativeCallContext<'a>, $($param),*) -> RhaiResultOf<RET> + SendSync + 'static,
             $($par: Variant + Clone,)*
             RET: Variant + Clone
-        > RegisterNativeFunction<($($mark,)*), $n, true, RET, true> for FN {
+        > RhaiNativeFunc<($($mark,)*), $n, true, RET, true> for FN {
             #[inline(always)] fn param_types() -> [TypeId;$n] { [$(TypeId::of::<$par>()),*] }
             #[cfg(feature = "metadata")] #[inline(always)] fn param_names() -> [&'static str;$n] { [$(type_name::<$param>()),*] }
             #[cfg(feature = "metadata")] #[inline(always)] fn return_type_name() -> &'static str { type_name::<RhaiResultOf<RET>>() }
-            #[inline(always)] fn into_callable_function(self, fn_name: Identifier, is_pure: bool, is_volatile: bool) -> CallableFunction {
-                CallableFunction::$abi { func: Shared::new(move |ctx: Option<NativeCallContext>, args: &mut FnCallArgs| {
+            #[inline(always)] fn into_callable_function(self, is_pure: bool, is_volatile: bool) -> RhaiFunc {
+                RhaiFunc::$abi { func: Shared::new(move |ctx: Option<NativeCallContext>, args: &mut FnCallArgs| {
                     let ctx = ctx.unwrap();
 
                     // The arguments are assumed to be of the correct number and types!
@@ -242,7 +230,7 @@ macro_rules! def_register {
     ($p0:ident:$n0:expr $(, $p:ident: $n:expr)*) => {
         def_register!(imp Pure   : $n0 ; $p0 => $p0      => $p0      => $p0      => by_value $(, $p => $p => $p => $p => by_value)*);
         def_register!(imp Method : $n0 ; $p0 => &mut $p0 => Mut<$p0> => &mut $p0 => by_ref   $(, $p => $p => $p => $p => by_value)*);
-        //                ^ CallableFunction constructor
+        //                ^ RhaiFunc constructor
         //                         ^ number of arguments                            ^ first parameter passed through
         //                                                                                       ^ others passed by value (by_value)
 
diff --git a/src/func/script.rs b/src/func/script.rs
index ed98d39c4..719593fd9 100644
--- a/src/func/script.rs
+++ b/src/func/script.rs
@@ -2,9 +2,8 @@
 #![cfg(not(feature = "no_function"))]
 
 use super::call::FnCallArgs;
-use crate::ast::ScriptFnDef;
+use crate::ast::{EncapsulatedEnviron, ScriptFuncDef};
 use crate::eval::{Caches, GlobalRuntimeState};
-use crate::func::EncapsulatedEnviron;
 use crate::{Dynamic, Engine, Position, RhaiResult, Scope, ERR};
 #[cfg(feature = "no_std")]
 use std::prelude::v1::*;
@@ -29,7 +28,7 @@ impl Engine {
         scope: &mut Scope,
         mut this_ptr: Option<&mut Dynamic>,
         _environ: Option<&EncapsulatedEnviron>,
-        fn_def: &ScriptFnDef,
+        fn_def: &ScriptFuncDef,
         args: &mut FnCallArgs,
         rewind_scope: bool,
         pos: Position,
diff --git a/src/lib.rs b/src/lib.rs
index 4f270ec68..44cbfb53d 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -242,8 +242,8 @@ pub use eval::EvalContext;
 #[cfg(not(feature = "no_object"))]
 use func::calc_typed_method_hash;
 use func::{calc_fn_hash, calc_fn_hash_full, calc_var_hash};
-pub use func::{plugin, FuncArgs, NativeCallContext, RegisterNativeFunction};
-pub use module::{FnNamespace, Module};
+pub use func::{plugin, FuncArgs, NativeCallContext, RhaiNativeFunc};
+pub use module::{FnNamespace, FuncRegistration, Module};
 pub use packages::string_basic::{FUNC_TO_DEBUG, FUNC_TO_STRING};
 pub use rhai_codegen::*;
 #[cfg(not(feature = "no_time"))]
@@ -359,8 +359,9 @@ pub use api::default_limits;
 
 #[cfg(feature = "internals")]
 pub use ast::{
-    ASTFlags, ASTNode, BinaryExpr, ConditionalExpr, Expr, FlowControl, FnCallExpr, FnCallHashes,
-    Ident, OpAssignment, RangeCase, ScriptFnDef, Stmt, StmtBlock, SwitchCasesCollection,
+    ASTFlags, ASTNode, BinaryExpr, EncapsulatedEnviron, Expr, FlowControl, FnCallExpr,
+    FnCallHashes, Ident, OpAssignment, RangeCase, ScriptFuncDef, Stmt, StmtBlock,
+    SwitchCasesCollection,
 };
 
 #[cfg(feature = "internals")]
@@ -371,15 +372,12 @@ pub use ast::CustomExpr;
 #[cfg(not(feature = "no_module"))]
 pub use ast::Namespace;
 
-#[cfg(feature = "internals")]
-pub use func::EncapsulatedEnviron;
-
 #[cfg(feature = "internals")]
 pub use eval::{Caches, FnResolutionCache, FnResolutionCacheEntry, GlobalRuntimeState};
 
 #[cfg(feature = "internals")]
 #[allow(deprecated)]
-pub use func::{locked_read, locked_write, CallableFunction, NativeCallContextStore};
+pub use func::{locked_read, locked_write, NativeCallContextStore, RhaiFunc};
 
 #[cfg(feature = "internals")]
 #[cfg(feature = "metadata")]
diff --git a/src/module/mod.rs b/src/module/mod.rs
index bb39e004a..4a01c9e6e 100644
--- a/src/module/mod.rs
+++ b/src/module/mod.rs
@@ -4,13 +4,12 @@
 use crate::api::formatting::format_type;
 use crate::ast::FnAccess;
 use crate::func::{
-    shared_take_or_clone, CallableFunction, FnCallArgs, IteratorFn, RegisterNativeFunction,
-    SendSync, StraightHashMap,
+    shared_take_or_clone, FnIterator, RhaiFunc, RhaiNativeFunc, SendSync, StraightHashMap,
 };
 use crate::types::{dynamic::Variant, BloomFilterU64, CustomTypeInfo, CustomTypesCollection};
 use crate::{
-    calc_fn_hash, calc_fn_hash_full, Dynamic, Identifier, ImmutableString, NativeCallContext,
-    RhaiResultOf, Shared, SharedModule, SmartString,
+    calc_fn_hash, calc_fn_hash_full, Dynamic, FnArgsVec, Identifier, ImmutableString, RhaiResultOf,
+    Shared, SharedModule, SmartString,
 };
 use bitflags::bitflags;
 #[cfg(feature = "no_std")]
@@ -71,9 +70,9 @@ impl FnNamespace {
 }
 
 /// A type containing the metadata of a single registered function.
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, Eq, PartialEq, Hash)]
 #[non_exhaustive]
-pub struct FuncInfoMetadata {
+pub struct FuncMetadata {
     /// Hash value.
     pub hash: u64,
     /// Function namespace.
@@ -82,53 +81,40 @@ pub struct FuncInfoMetadata {
     pub access: FnAccess,
     /// Function name.
     pub name: Identifier,
-    #[cfg(not(feature = "no_object"))]
-    /// Type of `this` pointer, if any.
-    pub this_type: Option<ImmutableString>,
     /// Number of parameters.
     pub num_params: usize,
     /// Parameter types (if applicable).
-    pub param_types: Box<[TypeId]>,
+    pub param_types: FnArgsVec<TypeId>,
     /// Parameter names and types (if available).
     #[cfg(feature = "metadata")]
-    pub params_info: Box<[Identifier]>,
+    pub params_info: FnArgsVec<Identifier>,
     /// Return type name.
     #[cfg(feature = "metadata")]
     pub return_type: Identifier,
     /// Comments.
     #[cfg(feature = "metadata")]
-    pub comments: Box<[SmartString]>,
-}
-
-/// A type containing a single registered function.
-#[derive(Debug, Clone)]
-pub struct FuncInfo {
-    /// Function instance.
-    pub func: CallableFunction,
-    /// Function metadata.
-    pub metadata: Box<FuncInfoMetadata>,
+    pub comments: crate::StaticVec<SmartString>,
 }
 
-impl FuncInfo {
+impl FuncMetadata {
     /// _(metadata)_ Generate a signature of the function.
     /// Exported under the `metadata` feature only.
     #[cfg(feature = "metadata")]
     #[must_use]
     pub fn gen_signature(&self) -> String {
-        let mut signature = format!("{}(", self.metadata.name);
+        let mut signature = format!("{}(", self.name);
 
-        let return_type = format_type(&self.metadata.return_type, true);
+        let return_type = format_type(&self.return_type, true);
 
-        if self.metadata.params_info.is_empty() {
-            for x in 0..self.metadata.num_params {
+        if self.params_info.is_empty() {
+            for x in 0..self.num_params {
                 signature.push('_');
-                if x < self.metadata.num_params - 1 {
+                if x < self.num_params - 1 {
                     signature.push_str(", ");
                 }
             }
         } else {
             let params = self
-                .metadata
                 .params_info
                 .iter()
                 .map(|param| {
@@ -148,7 +134,7 @@ impl FuncInfo {
         }
         signature.push(')');
 
-        if !self.func.is_script() && !return_type.is_empty() {
+        if !return_type.is_empty() {
             signature.push_str(" -> ");
             signature.push_str(&return_type);
         }
@@ -178,6 +164,162 @@ pub fn calc_native_fn_hash<'a>(
     )
 }
 
+/// Type for fine-tuned module function registration.
+#[derive(Debug, Clone, Eq, PartialEq, Hash)]
+pub struct FuncRegistration {
+    metadata: FuncMetadata,
+}
+
+impl FuncRegistration {
+    /// Create a new [`FuncRegistration`].
+    ///
+    /// ```
+    /// # use rhai::{Module, FuncRegistration, FnNamespace};
+    /// let mut module = Module::new();
+    ///
+    /// fn inc(x: i64) -> i64 { x + 1 }
+    ///
+    /// let f = FuncRegistration::new("inc")
+    ///     .with_namespace(FnNamespace::Global)
+    ///     .set_into_module(&mut module, inc);
+    ///
+    /// let hash = f.hash;
+    ///
+    /// assert!(module.contains_fn(hash));
+    /// ```
+    pub fn new(name: impl Into<Identifier>) -> Self {
+        Self {
+            metadata: FuncMetadata {
+                hash: 0,
+                name: name.into(),
+                namespace: FnNamespace::Internal,
+                access: FnAccess::Public,
+                num_params: 0,
+                param_types: <_>::default(),
+                #[cfg(feature = "metadata")]
+                params_info: <_>::default(),
+                #[cfg(feature = "metadata")]
+                return_type: "".into(),
+                #[cfg(feature = "metadata")]
+                comments: <_>::default(),
+            },
+        }
+    }
+    /// Set the [namespace][`FnNamespace`] of the function.
+    pub fn with_namespace(mut self, namespace: FnNamespace) -> Self {
+        self.metadata.namespace = namespace;
+        self
+    }
+    /// _(metadata)_ Set the function's parameter names and/or types.
+    /// Exported under the `metadata` feature only.
+    #[cfg(feature = "metadata")]
+    pub fn with_params_info<S: AsRef<str>>(mut self, params: impl IntoIterator<Item = S>) -> Self {
+        self.metadata.params_info = params.into_iter().map(|s| s.as_ref().into()).collect();
+        self
+    }
+    /// _(metadata)_ Set the function's doc-comments.
+    /// Exported under the `metadata` feature only.
+    #[cfg(feature = "metadata")]
+    pub fn with_comments<S: AsRef<str>>(mut self, comments: impl IntoIterator<Item = S>) -> Self {
+        self.metadata.comments = comments.into_iter().map(|s| s.as_ref().into()).collect();
+        self
+    }
+    /// Register the function into the specified [`Module`].
+    ///
+    /// # Assumptions
+    ///
+    /// * The function is assumed to be _pure_ (so it can be called on constants) unless it is a property setter or an index setter.
+    ///
+    /// * The function is assumed to be _volatile_ -- i.e. it does not guarantee the same result for the same input(s).
+    #[inline]
+    pub fn set_into_module<A: 'static, const N: usize, const X: bool, R, const F: bool, FUNC>(
+        self,
+        module: &mut Module,
+        func: FUNC,
+    ) -> &FuncMetadata
+    where
+        R: Variant + Clone,
+        FUNC: RhaiNativeFunc<A, N, X, R, F> + SendSync + 'static,
+    {
+        let is_pure = true;
+
+        #[cfg(any(not(feature = "no_index"), not(feature = "no_object")))]
+        let is_pure =
+            is_pure && (FUNC::num_params() != 3 || self.metadata.name != crate::engine::FN_IDX_SET);
+        #[cfg(not(feature = "no_object"))]
+        let is_pure = is_pure
+            && (FUNC::num_params() != 2 || !self.metadata.name.starts_with(crate::engine::FN_SET));
+
+        let func = func.into_callable_function(is_pure, true);
+        self.set_into_module_raw(module, FUNC::param_types(), func)
+    }
+    /// Register the function into the specified [`Module`].
+    #[inline]
+    pub fn set_into_module_raw(
+        self,
+        module: &mut Module,
+        arg_types: impl AsRef<[TypeId]>,
+        func: RhaiFunc,
+    ) -> &FuncMetadata {
+        let mut f = self.metadata;
+
+        f.num_params = arg_types.as_ref().len();
+        f.param_types.extend(arg_types.as_ref().iter().copied());
+
+        let is_method = func.is_method();
+
+        f.param_types
+            .iter_mut()
+            .enumerate()
+            .for_each(|(i, type_id)| *type_id = Module::map_type(!is_method || i > 0, *type_id));
+
+        let is_dynamic = f
+            .param_types
+            .iter()
+            .any(|&type_id| type_id == TypeId::of::<Dynamic>());
+
+        #[cfg(feature = "metadata")]
+        if f.params_info.len() > f.param_types.len() {
+            f.return_type = f.params_info.pop().unwrap();
+        }
+
+        let hash_base = calc_fn_hash(None, &f.name, f.param_types.len());
+        let hash_fn = calc_fn_hash_full(hash_base, f.param_types.iter().copied());
+        f.hash = hash_fn;
+
+        // Catch hash collisions in testing environment only.
+        #[cfg(feature = "testing-environ")]
+        if let Some(fx) = module.functions.as_ref().and_then(|f| f.get(&hash_base)) {
+            unreachable!(
+                "Hash {} already exists when registering function {}:\n{:#?}",
+                hash_base, f.name, fx
+            );
+        }
+
+        if is_dynamic {
+            module.dynamic_functions_filter.mark(hash_base);
+        }
+
+        module
+            .flags
+            .remove(ModuleFlags::INDEXED | ModuleFlags::INDEXED_GLOBAL_FUNCTIONS);
+
+        let entry = match module
+            .functions
+            .get_or_insert_with(|| new_hash_map(FN_MAP_SIZE))
+            .entry(hash_fn)
+        {
+            Entry::Occupied(mut entry) => {
+                entry.insert((func, f.into()));
+                entry.into_mut()
+            }
+            Entry::Vacant(entry) => entry.insert((func, f.into())),
+        };
+
+        &*entry.1
+    }
+}
+
 bitflags! {
     /// Bit-flags containing all status for [`Module`].
     #[derive(PartialEq, Eq, PartialOrd, Ord, Hash, Debug, Clone, Copy)]
@@ -211,16 +353,16 @@ pub struct Module {
     /// Flattened collection of all [`Module`] variables, including those in sub-modules.
     all_variables: Option<StraightHashMap<Dynamic>>,
     /// Functions (both native Rust and scripted).
-    functions: Option<StraightHashMap<FuncInfo>>,
+    functions: Option<StraightHashMap<(RhaiFunc, Box<FuncMetadata>)>>,
     /// Flattened collection of all functions, native Rust and scripted.
     /// including those in sub-modules.
-    all_functions: Option<StraightHashMap<CallableFunction>>,
+    all_functions: Option<StraightHashMap<RhaiFunc>>,
     /// Bloom filter on native Rust functions (in scripted hash format) that contain [`Dynamic`] parameters.
     dynamic_functions_filter: BloomFilterU64,
     /// Iterator functions, keyed by the type producing the iterator.
-    type_iterators: BTreeMap<TypeId, Shared<IteratorFn>>,
+    type_iterators: BTreeMap<TypeId, Shared<FnIterator>>,
     /// Flattened collection of iterator functions, including those in sub-modules.
-    all_type_iterators: BTreeMap<TypeId, Shared<IteratorFn>>,
+    all_type_iterators: BTreeMap<TypeId, Shared<FnIterator>>,
     /// Flags.
     pub(crate) flags: ModuleFlags,
 }
@@ -257,7 +399,12 @@ impl fmt::Debug for Module {
                 "functions",
                 &self
                     .iter_fn()
-                    .map(|f| f.func.to_string())
+                    .map(|(_f, _m)| {
+                        #[cfg(not(feature = "metadata"))]
+                        return _f.to_string();
+                        #[cfg(feature = "metadata")]
+                        return _m.gen_signature();
+                    })
                     .collect::<Vec<_>>(),
             )
             .field("flags", &self.flags);
@@ -270,7 +417,7 @@ impl fmt::Debug for Module {
 }
 
 #[cfg(not(feature = "no_function"))]
-impl<T: IntoIterator<Item = Shared<crate::ast::ScriptFnDef>>> From<T> for Module {
+impl<T: IntoIterator<Item = Shared<crate::ast::ScriptFuncDef>>> From<T> for Module {
     fn from(iter: T) -> Self {
         let mut module = Self::new();
         iter.into_iter().for_each(|fn_def| {
@@ -709,11 +856,12 @@ impl Module {
     #[inline]
     pub fn gen_fn_signatures(&self) -> impl Iterator<Item = String> + '_ {
         self.iter_fn()
-            .filter(|&f| match f.metadata.access {
+            .map(|(_, f)| f)
+            .filter(|&f| match f.access {
                 FnAccess::Public => true,
                 FnAccess::Private => false,
             })
-            .map(FuncInfo::gen_signature)
+            .map(FuncMetadata::gen_signature)
     }
 
     /// Does a variable exist in the [`Module`]?
@@ -821,7 +969,7 @@ impl Module {
     /// If there is an existing function of the same name and number of arguments, it is replaced.
     #[cfg(not(feature = "no_function"))]
     #[inline]
-    pub fn set_script_fn(&mut self, fn_def: impl Into<Shared<crate::ast::ScriptFnDef>>) -> u64 {
+    pub fn set_script_fn(&mut self, fn_def: impl Into<Shared<crate::ast::ScriptFuncDef>>) -> u64 {
         let fn_def = fn_def.into();
 
         // None + function name + number of arguments.
@@ -849,34 +997,24 @@ impl Module {
             );
         }
 
-        #[cfg(feature = "metadata")]
-        let params_info = fn_def.params.iter().map(Into::into).collect();
+        let metadata = FuncMetadata {
+            hash: hash_script,
+            name: fn_def.name.as_str().into(),
+            namespace,
+            access: fn_def.access,
+            num_params,
+            param_types: FnArgsVec::new_const(),
+            #[cfg(feature = "metadata")]
+            params_info: fn_def.params.iter().map(Into::into).collect(),
+            #[cfg(feature = "metadata")]
+            return_type: <_>::default(),
+            #[cfg(feature = "metadata")]
+            comments: crate::StaticVec::new_const(),
+        };
 
         self.functions
             .get_or_insert_with(|| new_hash_map(FN_MAP_SIZE))
-            .insert(
-                hash_script,
-                FuncInfo {
-                    metadata: FuncInfoMetadata {
-                        hash: hash_script,
-                        name: fn_def.name.as_str().into(),
-                        namespace,
-                        access: fn_def.access,
-                        #[cfg(not(feature = "no_object"))]
-                        this_type: fn_def.this_type.clone(),
-                        num_params,
-                        param_types: <_>::default(),
-                        #[cfg(feature = "metadata")]
-                        params_info,
-                        #[cfg(feature = "metadata")]
-                        return_type: "".into(),
-                        #[cfg(feature = "metadata")]
-                        comments: <_>::default(),
-                    }
-                    .into(),
-                    func: fn_def.into(),
-                },
-            );
+            .insert(hash_script, (fn_def.into(), metadata.into()));
 
         self.flags
             .remove(ModuleFlags::INDEXED | ModuleFlags::INDEXED_GLOBAL_FUNCTIONS);
@@ -893,13 +1031,13 @@ impl Module {
         &self,
         name: impl AsRef<str>,
         num_params: usize,
-    ) -> Option<&Shared<crate::ast::ScriptFnDef>> {
+    ) -> Option<&Shared<crate::ast::ScriptFuncDef>> {
         self.functions.as_ref().and_then(|lib| {
             let name = name.as_ref();
 
             lib.values()
-                .find(|&f| f.metadata.num_params == num_params && f.metadata.name == name)
-                .and_then(|f| f.func.get_script_fn_def())
+                .find(|(_, f)| f.num_params == num_params && f.name == name)
+                .and_then(|(f, _)| f.get_script_fn_def())
         })
     }
 
@@ -1004,93 +1142,61 @@ impl Module {
             .map_or(false, |m| m.contains_key(&hash_fn))
     }
 
-    /// _(metadata)_ Update the metadata (parameter names/types and return type) of a registered function.
+    /// _(metadata)_ Update the metadata (parameter names/types, return type and doc-comments) of a registered function.
     /// Exported under the `metadata` feature only.
     ///
     /// The [`u64`] hash is returned by the [`set_native_fn`][Module::set_native_fn] call.
     ///
-    /// ## Parameter Names and Types
-    ///
-    /// Each parameter name/type pair should be a single string of the format: `var_name: type`.
+    /// # Deprecated
     ///
-    /// ## Return Type
+    /// This method is deprecated.
+    /// Use the [`FuncRegistration`] API instead.
     ///
-    /// The _last entry_ in the list should be the _return type_ of the function.
-    /// In other words, the number of entries should be one larger than the number of parameters.
+    /// This method will be removed in the next major version.
+    #[deprecated(since = "1.17.0", note = "use the `FuncRegistration` API instead")]
     #[cfg(feature = "metadata")]
     #[inline]
-    pub fn update_fn_metadata<S: Into<Identifier>>(
+    pub fn update_fn_metadata_with_comments<A: Into<Identifier>, C: Into<SmartString>>(
         &mut self,
         hash_fn: u64,
-        arg_names: impl IntoIterator<Item = S>,
+        arg_names: impl IntoIterator<Item = A>,
+        comments: impl IntoIterator<Item = C>,
     ) -> &mut Self {
-        let mut param_names = arg_names.into_iter().map(Into::into).collect::<Vec<_>>();
-
-        if let Some(f) = self.functions.as_mut().and_then(|m| m.get_mut(&hash_fn)) {
-            let (param_names, return_type_name) = if param_names.len() > f.metadata.num_params {
-                let return_type = param_names.pop().unwrap();
-                (param_names, return_type)
+        let mut params_info = arg_names
+            .into_iter()
+            .map(Into::into)
+            .collect::<FnArgsVec<_>>();
+
+        if let Some((_, f)) = self.functions.as_mut().and_then(|m| m.get_mut(&hash_fn)) {
+            let (params_info, return_type_name) = if params_info.len() > f.num_params {
+                let return_type = params_info.pop().unwrap();
+                (params_info, return_type)
             } else {
-                (param_names, crate::SmartString::new_const())
+                (params_info, crate::SmartString::new_const())
             };
-            f.metadata.params_info = param_names.into_boxed_slice();
-            f.metadata.return_type = return_type_name;
+            f.params_info = params_info;
+            f.return_type = return_type_name;
+            f.comments = comments.into_iter().map(Into::into).collect();
         }
 
         self
     }
 
-    /// _(metadata)_ Update the metadata (parameter names/types, return type and doc-comments) of a registered function.
-    /// Exported under the `metadata` feature only.
+    /// Update the namespace of a registered function.
     ///
     /// The [`u64`] hash is returned by the [`set_native_fn`][Module::set_native_fn] call.
     ///
-    /// ## Parameter Names and Types
-    ///
-    /// Each parameter name/type pair should be a single string of the format: `var_name: type`.
-    ///
-    /// ## Return Type
-    ///
-    /// The _last entry_ in the list should be the _return type_ of the function. In other words,
-    /// the number of entries should be one larger than the number of parameters.
-    ///
-    /// ## Comments
-    ///
-    /// Block doc-comments should be kept in a separate string slice.
-    ///
-    /// Line doc-comments should be merged, with line-breaks, into a single string slice without a final termination line-break.
-    ///
-    /// Leading white-spaces should be stripped, and each string slice always starts with the corresponding
-    /// doc-comment leader: `///` or `/**`.
+    /// # Deprecated
     ///
-    /// Each line in non-block doc-comments should start with `///`.
-    #[cfg(feature = "metadata")]
-    #[inline]
-    pub fn update_fn_metadata_with_comments<A: Into<Identifier>, C: Into<SmartString>>(
-        &mut self,
-        hash_fn: u64,
-        arg_names: impl IntoIterator<Item = A>,
-        comments: impl IntoIterator<Item = C>,
-    ) -> &mut Self {
-        self.update_fn_metadata(hash_fn, arg_names);
-
-        self.functions
-            .as_mut()
-            .and_then(|m| m.get_mut(&hash_fn))
-            .unwrap()
-            .metadata
-            .comments = comments.into_iter().map(Into::into).collect();
-
-        self
-    }
-
-    /// Update the namespace of a registered function.
+    /// This method is deprecated.
+    /// Use the [`FuncRegistration`] API instead.
     ///
-    /// The [`u64`] hash is returned by the [`set_native_fn`][Module::set_native_fn] call.
+    /// This method will be removed in the next major version.
+    #[deprecated(since = "1.17.0", note = "use the `FuncRegistration` API instead")]
     #[inline]
     pub fn update_fn_namespace(&mut self, hash_fn: u64, namespace: FnNamespace) -> &mut Self {
-        if let Some(f) = self.functions.as_mut().and_then(|m| m.get_mut(&hash_fn)) {
-            f.metadata.namespace = namespace;
+        if let Some((_, f)) = self.functions.as_mut().and_then(|m| m.get_mut(&hash_fn)) {
+            f.namespace = namespace;
             self.flags
                 .remove(ModuleFlags::INDEXED | ModuleFlags::INDEXED_GLOBAL_FUNCTIONS);
         }
@@ -1116,278 +1222,15 @@ impl Module {
         type_id
     }
 
-    /// Set a native Rust function into the [`Module`], returning a [`u64`] hash key.
-    ///
-    /// If there is an existing Rust function of the same hash, it is replaced.
-    ///
-    /// # WARNING - Low Level API
-    ///
-    /// This function is very low level.
-    ///
-    /// ## Parameter Names and Types
-    ///
-    /// Each parameter name/type pair should be a single string of the format: `var_name: type`.
-    ///
-    /// ## Return Type
-    ///
-    /// The _last entry_ in the list should be the _return type_ of the function.
-    /// In other words, the number of entries should be one larger than the number of parameters.
+    /// Set a native Rust function into the [`Module`] based on a [`FuncRegistration`].
     #[inline(always)]
-    pub fn set_fn(
+    pub fn set_fn_raw_with_options(
         &mut self,
-        name: impl Into<Identifier>,
-        namespace: FnNamespace,
-        access: FnAccess,
-        arg_names: Option<&[&str]>,
+        options: FuncRegistration,
         arg_types: impl AsRef<[TypeId]>,
-        func: CallableFunction,
-    ) -> u64 {
-        const EMPTY: &[&str] = &[];
-        let arg_names = arg_names.unwrap_or(EMPTY);
-
-        self._set_fn(name, namespace, access, arg_names, arg_types, EMPTY, func)
-            .metadata
-            .hash
-    }
-
-    /// _(metadata)_ Set a native Rust function into the [`Module`], returning a [`u64`] hash key.
-    /// Exported under the `metadata` feature only.
-    ///
-    /// If there is an existing Rust function of the same hash, it is replaced.
-    ///
-    /// # WARNING - Low Level API
-    ///
-    /// This function is very low level.
-    ///
-    /// ## Parameter Names and Types
-    ///
-    /// Each parameter name/type pair should be a single string of the format: `var_name: type`.
-    ///
-    /// ## Return Type
-    ///
-    /// The _last entry_ in the list should be the _return type_ of the function.
-    /// In other words, the number of entries should be one larger than the number of parameters.
-    ///
-    /// ## Comments
-    ///
-    /// Block doc-comments should be kept in a separate string slice.
-    ///
-    /// Line doc-comments should be merged, with line-breaks, into a single string slice without a final termination line-break.
-    ///
-    /// Leading white-spaces should be stripped, and each string slice always starts with the corresponding
-    /// doc-comment leader: `///` or `/**`.
-    ///
-    /// Each line in non-block doc-comments should start with `///`.
-    #[cfg(feature = "metadata")]
-    #[inline(always)]
-    pub fn set_fn_with_comments<C: AsRef<str>>(
-        &mut self,
-        name: impl Into<Identifier>,
-        namespace: FnNamespace,
-        access: FnAccess,
-        arg_names: Option<&[&str]>,
-        arg_types: impl AsRef<[TypeId]>,
-        comments: impl IntoIterator<Item = C>,
-        func: CallableFunction,
-    ) -> u64 {
-        let arg_names = arg_names.unwrap_or(&[]);
-        self._set_fn(
-            name, namespace, access, arg_names, arg_types, comments, func,
-        )
-        .metadata
-        .hash
-    }
-
-    /// Set a native Rust function into the [`Module`], returning a [`u64`] hash key.
-    ///
-    /// If there is an existing Rust function of the same hash, it is replaced.
-    #[inline]
-    fn _set_fn<A: AsRef<str>, C: AsRef<str>>(
-        &mut self,
-        name: impl Into<Identifier>,
-        namespace: FnNamespace,
-        access: FnAccess,
-        arg_names: impl IntoIterator<Item = A>,
-        arg_types: impl AsRef<[TypeId]>,
-        comments: impl IntoIterator<Item = C>,
-        func: CallableFunction,
-    ) -> &mut FuncInfo {
-        let _arg_names = arg_names;
-        let _comments = comments;
-        let is_method = func.is_method();
-
-        let param_types = arg_types
-            .as_ref()
-            .iter()
-            .enumerate()
-            .map(|(i, &type_id)| Self::map_type(!is_method || i > 0, type_id))
-            .collect::<Vec<_>>();
-
-        let is_dynamic = param_types
-            .iter()
-            .any(|&type_id| type_id == TypeId::of::<Dynamic>());
-
-        #[cfg(feature = "metadata")]
-        let (param_names, return_type_name) = {
-            let mut names = _arg_names
-                .into_iter()
-                .map(|a| a.as_ref().into())
-                .collect::<Vec<_>>();
-            let return_type = if names.len() > param_types.len() {
-                names.pop().unwrap()
-            } else {
-                crate::SmartString::new_const()
-            };
-            names.shrink_to_fit();
-            (names, return_type)
-        };
-
-        let name = name.into();
-        let hash_base = calc_fn_hash(None, &name, param_types.len());
-        let hash_fn = calc_fn_hash_full(hash_base, param_types.iter().copied());
-
-        // Catch hash collisions in testing environment only.
-        #[cfg(feature = "testing-environ")]
-        if let Some(f) = self.functions.as_ref().and_then(|f| f.get(&hash_base)) {
-            unreachable!(
-                "Hash {} already exists when registering function {}:\n{:#?}",
-                hash_base, name, f
-            );
-        }
-
-        if is_dynamic {
-            self.dynamic_functions_filter.mark(hash_base);
-        }
-
-        self.flags
-            .remove(ModuleFlags::INDEXED | ModuleFlags::INDEXED_GLOBAL_FUNCTIONS);
-
-        let f = FuncInfo {
-            func,
-            metadata: FuncInfoMetadata {
-                hash: hash_fn,
-                name,
-                namespace,
-                access,
-                #[cfg(not(feature = "no_object"))]
-                this_type: None,
-                num_params: param_types.len(),
-                param_types: param_types.into_boxed_slice(),
-                #[cfg(feature = "metadata")]
-                params_info: param_names.into_boxed_slice(),
-                #[cfg(feature = "metadata")]
-                return_type: return_type_name,
-                #[cfg(feature = "metadata")]
-                comments: _comments.into_iter().map(|s| s.as_ref().into()).collect(),
-            }
-            .into(),
-        };
-
-        match self
-            .functions
-            .get_or_insert_with(|| new_hash_map(FN_MAP_SIZE))
-            .entry(hash_fn)
-        {
-            Entry::Occupied(mut entry) => {
-                entry.insert(f);
-                entry.into_mut()
-            }
-            Entry::Vacant(entry) => entry.insert(f),
-        }
-    }
-
-    /// Set a native Rust function into the [`Module`], returning a [`u64`] hash key.
-    ///
-    /// If there is a similar existing Rust function, it is replaced.
-    ///
-    /// # Assumptions
-    ///
-    /// * The function is assumed to be _non-pure_.
-    ///
-    /// * The function is assumed to be _volatile_ -- i.e. it does not guarantee the same result for the same input(s).
-    ///
-    /// # WARNING - Low Level API
-    ///
-    /// This function is very low level.
-    ///
-    /// # Arguments
-    ///
-    /// A list of [`TypeId`]'s is taken as the argument types.
-    ///
-    /// Arguments are simply passed in as a mutable array of [`&mut Dynamic`][Dynamic],
-    /// which is guaranteed to contain enough arguments of the correct types.
-    ///
-    /// The function is assumed to be a _method_, meaning that the first argument should not be consumed.
-    /// All other arguments can be consumed.
-    ///
-    /// To access a primary argument value (i.e. cloning is cheap), use: `args[n].as_xxx().unwrap()`
-    ///
-    /// To access an argument value and avoid cloning, use `args[n].take().cast::<T>()`.
-    /// Notice that this will _consume_ the argument, replacing it with `()`.
-    ///
-    /// To access the first mutable argument, use `args.get_mut(0).unwrap()`
-    ///
-    /// # Function Metadata
-    ///
-    /// No metadata for the function is registered. Use [`update_fn_metadata`][Module::update_fn_metadata] to add metadata.
-    ///
-    /// # Example
-    ///
-    /// ```
-    /// use rhai::{Module, FnNamespace, FnAccess};
-    ///
-    /// let mut module = Module::new();
-    /// let hash = module.set_raw_fn("double_or_not", FnNamespace::Internal, FnAccess::Public,
-    ///                 // Pass parameter types via a slice with TypeId's
-    ///                 &[std::any::TypeId::of::<i64>(), std::any::TypeId::of::<bool>()],
-    ///                 // Fixed closure signature
-    ///                 |context, args| {
-    ///                     // 'args' is guaranteed to be the right length and of the correct types
-    ///
-    ///                     // Get the second parameter by 'consuming' it
-    ///                     let double = args[1].take().cast::<bool>();
-    ///                     // Since it is a primary type, it can also be cheaply copied
-    ///                     let double = args[1].clone_cast::<bool>();
-    ///                     // Get a mutable reference to the first argument.
-    ///                     let mut x = args[0].write_lock::<i64>().unwrap();
-    ///
-    ///                     let orig = *x;
-    ///
-    ///                     if double {
-    ///                         *x *= 2;            // the first argument can be mutated
-    ///                     }
-    ///
-    ///                     Ok(orig)                // return RhaiResult<T>
-    ///                 });
-    ///
-    /// assert!(module.contains_fn(hash));
-    /// ```
-    #[inline(always)]
-    pub fn set_raw_fn<T: Variant + Clone>(
-        &mut self,
-        name: impl Into<Identifier>,
-        namespace: FnNamespace,
-        access: FnAccess,
-        arg_types: impl AsRef<[TypeId]>,
-        func: impl Fn(NativeCallContext, &mut FnCallArgs) -> RhaiResultOf<T> + SendSync + 'static,
-    ) -> u64 {
-        let f = move |ctx: Option<NativeCallContext>, args: &mut FnCallArgs| {
-            func(ctx.unwrap(), args).map(Dynamic::from)
-        };
-
-        self.set_fn(
-            name,
-            namespace,
-            access,
-            None,
-            arg_types,
-            CallableFunction::Method {
-                func: Shared::new(f),
-                has_context: true,
-                is_pure: false,
-                is_volatile: true,
-            },
-        )
+        func: RhaiFunc,
+    ) -> &FuncMetadata {
+        options.set_into_module_raw(self, arg_types, func)
     }
 
     /// Set a native Rust function into the [`Module`], returning a [`u64`] hash key.
@@ -1400,15 +1243,11 @@ impl Module {
     ///
     /// * The function is assumed to be _volatile_ -- i.e. it does not guarantee the same result for the same input(s).
     ///
-    /// # Function Namespace
+    /// * The function namespace is [`FnNamespace::Internal`].
     ///
-    /// The default function namespace is [`FnNamespace::Internal`].
-    /// Use [`update_fn_namespace`][Module::update_fn_namespace] to change it.
+    /// * No metadata for the function is registered.
     ///
-    /// # Function Metadata
-    ///
-    /// No metadata for the function is registered.
-    /// Use [`update_fn_metadata`][Module::update_fn_metadata] to add metadata.
+    /// To change this, use the [`FuncRegistration`] API instead.
     ///
     /// # Example
     ///
@@ -1419,34 +1258,16 @@ impl Module {
     /// assert!(module.contains_fn(hash));
     /// ```
     #[inline]
-    pub fn set_native_fn<A: 'static, const N: usize, const C: bool, T, F>(
+    pub fn set_native_fn<A: 'static, const N: usize, const X: bool, R, FUNC>(
         &mut self,
         name: impl Into<Identifier>,
-        func: F,
+        func: FUNC,
     ) -> u64
     where
-        T: Variant + Clone,
-        F: RegisterNativeFunction<A, N, C, T, true> + SendSync + 'static,
+        R: Variant + Clone,
+        FUNC: RhaiNativeFunc<A, N, X, R, true> + SendSync + 'static,
     {
-        let fn_name = name.into();
-        let is_pure = true;
-
-        #[cfg(any(not(feature = "no_index"), not(feature = "no_object")))]
-        let is_pure = is_pure && (F::num_params() != 3 || fn_name != crate::engine::FN_IDX_SET);
-        #[cfg(not(feature = "no_object"))]
-        let is_pure =
-            is_pure && (F::num_params() != 2 || !fn_name.starts_with(crate::engine::FN_SET));
-
-        let func = func.into_callable_function(fn_name.clone(), is_pure, true);
-
-        self.set_fn(
-            fn_name,
-            FnNamespace::Internal,
-            FnAccess::Public,
-            None,
-            F::param_types(),
-            func,
-        )
+        FuncRegistration::new(name).set_into_module(self, func).hash
     }
 
     /// Set a Rust getter function taking one mutable parameter, returning a [`u64`] hash key.
@@ -1461,7 +1282,8 @@ impl Module {
     /// # Function Metadata
     ///
     /// No metadata for the function is registered.
-    /// Use [`update_fn_metadata`][Module::update_fn_metadata] to add metadata.
+    ///
+    /// Use the [`FuncRegistration`] API instead to add metadata.
     ///
     /// # Example
     ///
@@ -1473,23 +1295,20 @@ impl Module {
     /// ```
     #[cfg(not(feature = "no_object"))]
     #[inline(always)]
-    pub fn set_getter_fn<A, const C: bool, T, F>(&mut self, name: impl AsRef<str>, func: F) -> u64
+    pub fn set_getter_fn<A, const X: bool, R, FUNC>(
+        &mut self,
+        name: impl AsRef<str>,
+        func: FUNC,
+    ) -> u64
     where
         A: Variant + Clone,
-        T: Variant + Clone,
-        F: RegisterNativeFunction<(Mut<A>,), 1, C, T, true> + SendSync + 'static,
+        R: Variant + Clone,
+        FUNC: RhaiNativeFunc<(Mut<A>,), 1, X, R, true> + SendSync + 'static,
     {
-        let fn_name = crate::engine::make_getter(name.as_ref());
-        let func = func.into_callable_function(fn_name.clone(), true, true);
-
-        self.set_fn(
-            fn_name,
-            FnNamespace::Global,
-            FnAccess::Public,
-            None,
-            F::param_types(),
-            func,
-        )
+        FuncRegistration::new(crate::engine::make_getter(name.as_ref()))
+            .with_namespace(FnNamespace::Global)
+            .set_into_module(self, func)
+            .hash
     }
 
     /// Set a Rust setter function taking two parameters (the first one mutable) into the [`Module`],
@@ -1505,7 +1324,8 @@ impl Module {
     /// # Function Metadata
     ///
     /// No metadata for the function is registered.
-    /// Use [`update_fn_metadata`][Module::update_fn_metadata] to add metadata.
+    ///
+    /// Use the [`FuncRegistration`] API instead to add metadata.
     ///
     /// # Example
     ///
@@ -1521,23 +1341,20 @@ impl Module {
     /// ```
     #[cfg(not(feature = "no_object"))]
     #[inline(always)]
-    pub fn set_setter_fn<A, const C: bool, T, F>(&mut self, name: impl AsRef<str>, func: F) -> u64
+    pub fn set_setter_fn<A, const X: bool, R, FUNC>(
+        &mut self,
+        name: impl AsRef<str>,
+        func: FUNC,
+    ) -> u64
     where
         A: Variant + Clone,
-        T: Variant + Clone,
-        F: RegisterNativeFunction<(Mut<A>, T), 2, C, (), true> + SendSync + 'static,
+        R: Variant + Clone,
+        FUNC: RhaiNativeFunc<(Mut<A>, R), 2, X, (), true> + SendSync + 'static,
     {
-        let fn_name = crate::engine::make_setter(name.as_ref());
-        let func = func.into_callable_function(fn_name.clone(), false, true);
-
-        self.set_fn(
-            fn_name,
-            FnNamespace::Global,
-            FnAccess::Public,
-            None,
-            F::param_types(),
-            func,
-        )
+        FuncRegistration::new(crate::engine::make_setter(name.as_ref()))
+            .with_namespace(FnNamespace::Global)
+            .set_into_module(self, func)
+            .hash
     }
 
     /// Set a pair of Rust getter and setter functions into the [`Module`], returning both [`u64`] hash keys.
@@ -1550,7 +1367,8 @@ impl Module {
     /// # Function Metadata
     ///
     /// No metadata for the function is registered.
-    /// Use [`update_fn_metadata`][Module::update_fn_metadata] to add metadata.
+    ///
+    /// Use the [`FuncRegistration`] API instead to add metadata.
     ///
     /// # Example
     ///
@@ -1572,14 +1390,14 @@ impl Module {
     #[inline(always)]
     pub fn set_getter_setter_fn<
         A: Variant + Clone,
-        const C1: bool,
-        const C2: bool,
-        T: Variant + Clone,
+        const X1: bool,
+        const X2: bool,
+        R: Variant + Clone,
     >(
         &mut self,
         name: impl AsRef<str>,
-        getter: impl RegisterNativeFunction<(Mut<A>,), 1, C1, T, true> + SendSync + 'static,
-        setter: impl RegisterNativeFunction<(Mut<A>, T), 2, C2, (), true> + SendSync + 'static,
+        getter: impl RhaiNativeFunc<(Mut<A>,), 1, X1, R, true> + SendSync + 'static,
+        setter: impl RhaiNativeFunc<(Mut<A>, R), 2, X2, (), true> + SendSync + 'static,
     ) -> (u64, u64) {
         (
             self.set_getter_fn(name.as_ref(), getter),
@@ -1605,7 +1423,8 @@ impl Module {
     /// # Function Metadata
     ///
     /// No metadata for the function is registered.
-    /// Use [`update_fn_metadata`][Module::update_fn_metadata] to add metadata.
+    ///
+    /// Use the [`FuncRegistration`] API instead to add metadata.
     ///
     /// # Example
     ///
@@ -1620,12 +1439,12 @@ impl Module {
     /// ```
     #[cfg(any(not(feature = "no_index"), not(feature = "no_object")))]
     #[inline]
-    pub fn set_indexer_get_fn<A, B, const C: bool, T, F>(&mut self, func: F) -> u64
+    pub fn set_indexer_get_fn<A, B, const X: bool, R, FUNC>(&mut self, func: FUNC) -> u64
     where
         A: Variant + Clone,
         B: Variant + Clone,
-        T: Variant + Clone,
-        F: RegisterNativeFunction<(Mut<A>, B), 2, C, T, true> + SendSync + 'static,
+        R: Variant + Clone,
+        FUNC: RhaiNativeFunc<(Mut<A>, B), 2, X, R, true> + SendSync + 'static,
     {
         #[cfg(not(feature = "no_index"))]
         assert!(
@@ -1645,14 +1464,10 @@ impl Module {
             "Cannot register indexer for strings."
         );
 
-        self.set_fn(
-            crate::engine::FN_IDX_GET,
-            FnNamespace::Global,
-            FnAccess::Public,
-            None,
-            F::param_types(),
-            func.into_callable_function(crate::engine::FN_IDX_GET.into(), true, true),
-        )
+        FuncRegistration::new(crate::engine::FN_IDX_GET)
+            .with_namespace(FnNamespace::Global)
+            .set_into_module(self, func)
+            .hash
     }
 
     /// Set a Rust index setter taking three parameters (the first one mutable) into the [`Module`],
@@ -1673,7 +1488,8 @@ impl Module {
     /// # Function Metadata
     ///
     /// No metadata for the function is registered.
-    /// Use [`update_fn_metadata`][Module::update_fn_metadata] to add metadata.
+    ///
+    /// Use the [`FuncRegistration`] API instead to add metadata.
     ///
     /// # Example
     ///
@@ -1688,12 +1504,12 @@ impl Module {
     /// ```
     #[cfg(any(not(feature = "no_index"), not(feature = "no_object")))]
     #[inline]
-    pub fn set_indexer_set_fn<A, B, const C: bool, T, F>(&mut self, func: F) -> u64
+    pub fn set_indexer_set_fn<A, B, const X: bool, R, FUNC>(&mut self, func: FUNC) -> u64
     where
         A: Variant + Clone,
         B: Variant + Clone,
-        T: Variant + Clone,
-        F: RegisterNativeFunction<(Mut<A>, B, T), 3, C, (), true> + SendSync + 'static,
+        R: Variant + Clone,
+        FUNC: RhaiNativeFunc<(Mut<A>, B, R), 3, X, (), true> + SendSync + 'static,
     {
         #[cfg(not(feature = "no_index"))]
         assert!(
@@ -1713,14 +1529,10 @@ impl Module {
             "Cannot register indexer for strings."
         );
 
-        self.set_fn(
-            crate::engine::FN_IDX_SET,
-            FnNamespace::Global,
-            FnAccess::Public,
-            None,
-            F::param_types(),
-            func.into_callable_function(crate::engine::FN_IDX_SET.into(), false, true),
-        )
+        FuncRegistration::new(crate::engine::FN_IDX_SET)
+            .with_namespace(FnNamespace::Global)
+            .set_into_module(self, func)
+            .hash
     }
 
     /// Set a pair of Rust index getter and setter functions into the [`Module`], returning both [`u64`] hash keys.
@@ -1739,7 +1551,8 @@ impl Module {
     /// # Function Metadata
     ///
     /// No metadata for the function is registered.
-    /// Use [`update_fn_metadata`][Module::update_fn_metadata] to add metadata.
+    ///
+    /// Use the [`FuncRegistration`] API instead to add metadata.
     ///
     /// # Example
     ///
@@ -1763,13 +1576,13 @@ impl Module {
     pub fn set_indexer_get_set_fn<
         A: Variant + Clone,
         B: Variant + Clone,
-        const C1: bool,
-        const C2: bool,
-        T: Variant + Clone,
+        const X1: bool,
+        const X2: bool,
+        R: Variant + Clone,
     >(
         &mut self,
-        get_fn: impl RegisterNativeFunction<(Mut<A>, B), 2, C1, T, true> + SendSync + 'static,
-        set_fn: impl RegisterNativeFunction<(Mut<A>, B, T), 3, C2, (), true> + SendSync + 'static,
+        get_fn: impl RhaiNativeFunc<(Mut<A>, B), 2, X1, R, true> + SendSync + 'static,
+        set_fn: impl RhaiNativeFunc<(Mut<A>, B, R), 3, X2, (), true> + SendSync + 'static,
     ) -> (u64, u64) {
         (
             self.set_indexer_get_fn(get_fn),
@@ -1782,11 +1595,11 @@ impl Module {
     /// The [`u64`] hash is returned by the [`set_native_fn`][Module::set_native_fn] call.
     #[inline]
     #[must_use]
-    pub(crate) fn get_fn(&self, hash_native: u64) -> Option<&CallableFunction> {
+    pub(crate) fn get_fn(&self, hash_native: u64) -> Option<&RhaiFunc> {
         self.functions
             .as_ref()
             .and_then(|m| m.get(&hash_native))
-            .map(|f| &f.func)
+            .map(|(f, _)| f)
     }
 
     /// Can the particular function with [`Dynamic`] parameter(s) exist in the [`Module`]?
@@ -1815,7 +1628,7 @@ impl Module {
     #[cfg(not(feature = "no_module"))]
     #[inline]
     #[must_use]
-    pub(crate) fn get_qualified_fn(&self, hash_qualified_fn: u64) -> Option<&CallableFunction> {
+    pub(crate) fn get_qualified_fn(&self, hash_qualified_fn: u64) -> Option<&RhaiFunc> {
         self.all_functions
             .as_ref()
             .and_then(|m| m.get(&hash_qualified_fn))
@@ -1958,14 +1771,8 @@ impl Module {
                 Some(ref mut m) => m.extend(
                     functions
                         .iter()
-                        .filter(|(.., f)| {
-                            _filter(
-                                f.metadata.namespace,
-                                f.metadata.access,
-                                f.func.is_script(),
-                                &f.metadata.name,
-                                f.metadata.num_params,
-                            )
+                        .filter(|(.., (f, m))| {
+                            _filter(m.namespace, m.access, f.is_script(), &m.name, m.num_params)
                         })
                         .map(|(&k, f)| (k, f.clone())),
                 ),
@@ -2001,14 +1808,9 @@ impl Module {
     ) -> &mut Self {
         self.functions = std::mem::take(&mut self.functions).map(|m| {
             m.into_iter()
-                .filter(|(.., f)| {
-                    if f.func.is_script() {
-                        filter(
-                            f.metadata.namespace,
-                            f.metadata.access,
-                            &f.metadata.name,
-                            f.metadata.num_params,
-                        )
+                .filter(|(.., (f, m))| {
+                    if f.is_script() {
+                        filter(m.namespace, m.access, &m.name, m.num_params)
                     } else {
                         false
                     }
@@ -2070,8 +1872,11 @@ impl Module {
     /// Get an iterator to the functions in the [`Module`].
     #[inline]
     #[allow(dead_code)]
-    pub(crate) fn iter_fn(&self) -> impl Iterator<Item = &FuncInfo> {
-        self.functions.iter().flat_map(StraightHashMap::values)
+    pub(crate) fn iter_fn(&self) -> impl Iterator<Item = (&RhaiFunc, &FuncMetadata)> {
+        self.functions
+            .iter()
+            .flat_map(StraightHashMap::values)
+            .map(|(f, m)| (f, &**m))
     }
 
     /// Get an iterator over all script-defined functions in the [`Module`].
@@ -2081,7 +1886,7 @@ impl Module {
     /// 2) Access mode ([`FnAccess::Public`] or [`FnAccess::Private`]).
     /// 3) Function name (as string slice).
     /// 4) Number of parameters.
-    /// 5) Shared reference to function definition [`ScriptFnDef`][crate::ast::ScriptFnDef].
+    /// 5) Shared reference to function definition [`ScriptFuncDef`][crate::ast::ScriptFuncDef].
     #[cfg(not(feature = "no_function"))]
     #[inline]
     pub(crate) fn iter_script_fn(
@@ -2092,16 +1897,16 @@ impl Module {
             FnAccess,
             &str,
             usize,
-            &Shared<crate::ast::ScriptFnDef>,
+            &Shared<crate::ast::ScriptFuncDef>,
         ),
     > + '_ {
-        self.iter_fn().filter(|&f| f.func.is_script()).map(|f| {
+        self.iter_fn().filter(|(f, _)| f.is_script()).map(|(f, m)| {
             (
-                f.metadata.namespace,
-                f.metadata.access,
-                f.metadata.name.as_str(),
-                f.metadata.num_params,
-                f.func.get_script_fn_def().expect("`ScriptFnDef`"),
+                m.namespace,
+                m.access,
+                m.name.as_str(),
+                m.num_params,
+                f.get_script_fn_def().expect("`ScriptFuncDef`"),
             )
         })
     }
@@ -2119,14 +1924,9 @@ impl Module {
     pub fn iter_script_fn_info(
         &self,
     ) -> impl Iterator<Item = (FnNamespace, FnAccess, &str, usize)> {
-        self.iter_fn().filter(|&f| f.func.is_script()).map(|f| {
-            (
-                f.metadata.namespace,
-                f.metadata.access,
-                f.metadata.name.as_str(),
-                f.metadata.num_params,
-            )
-        })
+        self.iter_fn()
+            .filter(|(f, _)| f.is_script())
+            .map(|(_, f)| (f.namespace, f.access, f.name.as_str(), f.num_params))
     }
 
     /// _(internals)_ Get an iterator over all script-defined functions in the [`Module`].
@@ -2137,7 +1937,7 @@ impl Module {
     /// 2) Access mode ([`FnAccess::Public`] or [`FnAccess::Private`]).
     /// 3) Function name (as string slice).
     /// 4) Number of parameters.
-    /// 5) _(internals)_ Shared reference to function definition [`ScriptFnDef`][crate::ast::ScriptFnDef].
+    /// 5) _(internals)_ Shared reference to function definition [`ScriptFuncDef`][crate::ast::ScriptFuncDef].
     #[cfg(not(feature = "no_function"))]
     #[cfg(feature = "internals")]
     #[inline(always)]
@@ -2149,7 +1949,7 @@ impl Module {
             FnAccess,
             &str,
             usize,
-            &Shared<crate::ast::ScriptFnDef>,
+            &Shared<crate::ast::ScriptFuncDef>,
         ),
     > {
         self.iter_script_fn()
@@ -2251,7 +2051,7 @@ impl Module {
         let _ = result?;
 
         // Encapsulated environment
-        let environ = Shared::new(crate::func::EncapsulatedEnviron {
+        let environ = Shared::new(crate::ast::EncapsulatedEnviron {
             #[cfg(not(feature = "no_function"))]
             lib: ast.shared_lib().clone(),
             imports,
@@ -2317,13 +2117,14 @@ impl Module {
             })
             .for_each(|f| {
                 let hash = module.set_script_fn(f.clone());
-                let f = module.functions.as_mut().unwrap().get_mut(&hash).unwrap();
-
-                // Encapsulate AST environment
-                if let CallableFunction::Script {
-                    environ: ref mut e, ..
-                } = f.func
+                if let (
+                    RhaiFunc::Script {
+                        environ: ref mut e, ..
+                    },
+                    _,
+                ) = module.functions.as_mut().unwrap().get_mut(&hash).unwrap()
                 {
+                    // Encapsulate AST environment
                     *e = Some(environ.clone());
                 }
             });
@@ -2359,8 +2160,8 @@ impl Module {
             module: &'a Module,
             path: &mut Vec<&'a str>,
             variables: &mut StraightHashMap<Dynamic>,
-            functions: &mut StraightHashMap<CallableFunction>,
-            type_iterators: &mut BTreeMap<TypeId, Shared<IteratorFn>>,
+            functions: &mut StraightHashMap<RhaiFunc>,
+            type_iterators: &mut BTreeMap<TypeId, Shared<FnIterator>>,
         ) -> bool {
             let mut contains_indexed_global_functions = false;
 
@@ -2395,40 +2196,38 @@ impl Module {
             }
 
             // Index all functions
-            for (&hash, f) in module.functions.iter().flatten() {
-                match f.metadata.namespace {
+            for (&hash, (f, m)) in module.functions.iter().flatten() {
+                match m.namespace {
                     FnNamespace::Global => {
                         // Catch hash collisions in testing environment only.
                         #[cfg(feature = "testing-environ")]
                         if let Some(fx) = functions.get(&hash) {
                             unreachable!(
                                 "Hash {} already exists when indexing function {:#?}:\n{:#?}",
-                                hash, f.func, fx
+                                hash, f, fx
                             );
                         }
 
                         // Flatten all functions with global namespace
-                        functions.insert(hash, f.func.clone());
+                        functions.insert(hash, f.clone());
                         contains_indexed_global_functions = true;
                     }
                     FnNamespace::Internal => (),
                 }
-                match f.metadata.access {
+                match m.access {
                     FnAccess::Public => (),
                     FnAccess::Private => continue, // Do not index private functions
                 }
 
-                if f.func.is_script() {
+                if f.is_script() {
                     #[cfg(not(feature = "no_function"))]
                     {
-                        let hash_script = crate::calc_fn_hash(
-                            path.iter().copied(),
-                            &f.metadata.name,
-                            f.metadata.num_params,
-                        );
+                        let hash_script =
+                            crate::calc_fn_hash(path.iter().copied(), &m.name, m.num_params);
                         #[cfg(not(feature = "no_object"))]
                         let hash_script = f
-                            .metadata
+                            .get_script_fn_def()
+                            .unwrap()
                             .this_type
                             .as_ref()
                             .map_or(hash_script, |this_type| {
@@ -2440,29 +2239,26 @@ impl Module {
                         if let Some(fx) = functions.get(&hash_script) {
                             unreachable!(
                                 "Hash {} already exists when indexing function {:#?}:\n{:#?}",
-                                hash_script, f.func, fx
+                                hash_script, f, fx
                             );
                         }
 
-                        functions.insert(hash_script, f.func.clone());
+                        functions.insert(hash_script, f.clone());
                     }
                 } else {
-                    let hash_fn = calc_native_fn_hash(
-                        path.iter().copied(),
-                        &f.metadata.name,
-                        &f.metadata.param_types,
-                    );
+                    let hash_fn =
+                        calc_native_fn_hash(path.iter().copied(), &m.name, &m.param_types);
 
                     // Catch hash collisions in testing environment only.
                     #[cfg(feature = "testing-environ")]
                     if let Some(fx) = functions.get(&hash_fn) {
                         unreachable!(
                             "Hash {} already exists when indexing function {:#?}:\n{:#?}",
-                            hash_fn, f.func, fx
+                            hash_fn, f, fx
                         );
                     }
 
-                    functions.insert(hash_fn, f.func.clone());
+                    functions.insert(hash_fn, f.clone());
                 }
             }
 
@@ -2592,14 +2388,14 @@ impl Module {
     #[cfg(not(feature = "no_module"))]
     #[inline]
     #[must_use]
-    pub(crate) fn get_qualified_iter(&self, id: TypeId) -> Option<&IteratorFn> {
+    pub(crate) fn get_qualified_iter(&self, id: TypeId) -> Option<&FnIterator> {
         self.all_type_iterators.get(&id).map(|f| &**f)
     }
 
     /// Get the specified type iterator.
     #[inline]
     #[must_use]
-    pub(crate) fn get_iter(&self, id: TypeId) -> Option<&IteratorFn> {
+    pub(crate) fn get_iter(&self, id: TypeId) -> Option<&FnIterator> {
         self.type_iterators.get(&id).map(|f| &**f)
     }
 }
diff --git a/src/optimizer.rs b/src/optimizer.rs
index ebc9f5209..4b0992c65 100644
--- a/src/optimizer.rs
+++ b/src/optimizer.rs
@@ -389,6 +389,16 @@ impl StmtBlock {
     }
 }
 
+/// Is this [`Expr`] a constant that is hashable?
+#[inline(always)]
+fn is_hashable_constant(expr: &Expr) -> bool {
+    match expr {
+        _ if !expr.is_constant() => false,
+        Expr::DynamicConstant(v, ..) => v.is_hashable(),
+        _ => false,
+    }
+}
+
 /// Optimize a [statement][Stmt].
 fn optimize_stmt(stmt: &mut Stmt, state: &mut OptimizerState, preserve_result: bool) {
     #[inline(always)]
@@ -505,7 +515,7 @@ fn optimize_stmt(stmt: &mut Stmt, state: &mut OptimizerState, preserve_result: b
         }
 
         // switch const { ... }
-        Stmt::Switch(x, pos) if x.0.is_constant() => {
+        Stmt::Switch(x, pos) if is_hashable_constant(&x.0) => {
             let (
                 match_expr,
                 SwitchCasesCollection {
@@ -529,23 +539,22 @@ fn optimize_stmt(stmt: &mut Stmt, state: &mut OptimizerState, preserve_result: b
                         let mut b = mem::take(&mut expressions[*index]);
                         cases.clear();
 
-                        if b.is_always_true() {
+                        if matches!(b.lhs, Expr::BoolConstant(true, ..)) {
                             // Promote the matched case
-                            let mut statements = Stmt::Expr(b.expr.take().into());
+                            let mut statements = Stmt::Expr(b.rhs.take().into());
                             optimize_stmt(&mut statements, state, true);
                             *stmt = statements;
                         } else {
                             // switch const { case if condition => stmt, _ => def } => if condition { stmt } else { def }
-                            optimize_expr(&mut b.condition, state, false);
+                            optimize_expr(&mut b.lhs, state, false);
 
                             let branch = def_case.map_or(StmtBlock::NONE, |index| {
-                                let mut def_stmt =
-                                    Stmt::Expr(expressions[index].expr.take().into());
+                                let mut def_stmt = Stmt::Expr(expressions[index].rhs.take().into());
                                 optimize_stmt(&mut def_stmt, state, true);
                                 def_stmt.into()
                             });
-                            let body = Stmt::Expr(b.expr.take().into()).into();
-                            let expr = b.condition.take();
+                            let body = Stmt::Expr(b.rhs.take().into()).into();
+                            let expr = b.lhs.take();
 
                             *stmt = Stmt::If(
                                 FlowControl { expr, body, branch }.into(),
@@ -560,9 +569,9 @@ fn optimize_stmt(stmt: &mut Stmt, state: &mut OptimizerState, preserve_result: b
                         for &index in case_blocks_list {
                             let mut b = mem::take(&mut expressions[index]);
 
-                            if b.is_always_true() {
+                            if matches!(b.lhs, Expr::BoolConstant(true, ..)) {
                                 // Promote the matched case
-                                let mut statements = Stmt::Expr(b.expr.take().into());
+                                let mut statements = Stmt::Expr(b.rhs.take().into());
                                 optimize_stmt(&mut statements, state, true);
                                 *stmt = statements;
                                 state.set_dirty();
@@ -579,31 +588,30 @@ fn optimize_stmt(stmt: &mut Stmt, state: &mut OptimizerState, preserve_result: b
                 if ranges.len() == 1
                     || ranges
                         .iter()
-                        .all(|r| expressions[r.index()].is_always_true())
+                        .all(|r| matches!(expressions[r.index()].lhs, Expr::BoolConstant(true, ..)))
                 {
                     if let Some(r) = ranges.iter().find(|r| r.contains(&value)) {
                         let range_block = &mut expressions[r.index()];
 
-                        if range_block.is_always_true() {
+                        if matches!(range_block.lhs, Expr::BoolConstant(true, ..)) {
                             // Promote the matched case
                             let block = &mut expressions[r.index()];
-                            let mut statements = Stmt::Expr(block.expr.take().into());
+                            let mut statements = Stmt::Expr(block.rhs.take().into());
                             optimize_stmt(&mut statements, state, true);
                             *stmt = statements;
                         } else {
-                            let mut expr = range_block.condition.take();
+                            let mut expr = range_block.lhs.take();
 
                             // switch const { range if condition => stmt, _ => def } => if condition { stmt } else { def }
                             optimize_expr(&mut expr, state, false);
 
                             let branch = def_case.map_or(StmtBlock::NONE, |index| {
-                                let mut def_stmt =
-                                    Stmt::Expr(expressions[index].expr.take().into());
+                                let mut def_stmt = Stmt::Expr(expressions[index].rhs.take().into());
                                 optimize_stmt(&mut def_stmt, state, true);
                                 def_stmt.into()
                             });
 
-                            let body = Stmt::Expr(expressions[r.index()].expr.take().into()).into();
+                            let body = Stmt::Expr(expressions[r.index()].rhs.take().into()).into();
 
                             *stmt = Stmt::If(
                                 FlowControl { expr, body, branch }.into(),
@@ -631,8 +639,8 @@ fn optimize_stmt(stmt: &mut Stmt, state: &mut OptimizerState, preserve_result: b
 
                     for r in ranges {
                         let b = &mut expressions[r.index()];
-                        optimize_expr(&mut b.condition, state, false);
-                        optimize_expr(&mut b.expr, state, false);
+                        optimize_expr(&mut b.lhs, state, false);
+                        optimize_expr(&mut b.rhs, state, false);
                     }
                     return;
                 }
@@ -643,7 +651,7 @@ fn optimize_stmt(stmt: &mut Stmt, state: &mut OptimizerState, preserve_result: b
 
             match def_case {
                 Some(index) => {
-                    let mut def_stmt = Stmt::Expr(expressions[*index].expr.take().into());
+                    let mut def_stmt = Stmt::Expr(expressions[*index].rhs.take().into());
                     optimize_stmt(&mut def_stmt, state, true);
                     *stmt = def_stmt;
                 }
@@ -667,11 +675,11 @@ fn optimize_stmt(stmt: &mut Stmt, state: &mut OptimizerState, preserve_result: b
 
             // Optimize blocks
             for b in &mut *expressions {
-                optimize_expr(&mut b.condition, state, false);
-                optimize_expr(&mut b.expr, state, false);
+                optimize_expr(&mut b.lhs, state, false);
+                optimize_expr(&mut b.rhs, state, false);
 
-                if b.is_always_false() && !b.expr.is_unit() {
-                    b.expr = Expr::Unit(b.expr.position());
+                if matches!(b.lhs, Expr::BoolConstant(false, ..)) && !b.rhs.is_unit() {
+                    b.rhs = Expr::Unit(b.rhs.position());
                     state.set_dirty();
                 }
             }
@@ -680,7 +688,7 @@ fn optimize_stmt(stmt: &mut Stmt, state: &mut OptimizerState, preserve_result: b
             cases.retain(|_, list| {
                 // Remove all entries that have false conditions
                 list.retain(|index| {
-                    if expressions[*index].is_always_false() {
+                    if matches!(expressions[*index].lhs, Expr::BoolConstant(false, ..)) {
                         state.set_dirty();
                         false
                     } else {
@@ -688,10 +696,9 @@ fn optimize_stmt(stmt: &mut Stmt, state: &mut OptimizerState, preserve_result: b
                     }
                 });
                 // Remove all entries after a `true` condition
-                if let Some(n) = list
-                    .iter()
-                    .position(|&index| expressions[index].is_always_true())
-                {
+                if let Some(n) = list.iter().position(|&index| {
+                    matches!(expressions[index].lhs, Expr::BoolConstant(true, ..))
+                }) {
                     if n + 1 < list.len() {
                         state.set_dirty();
                         list.truncate(n + 1);
@@ -708,7 +715,7 @@ fn optimize_stmt(stmt: &mut Stmt, state: &mut OptimizerState, preserve_result: b
 
             // Remove false ranges
             ranges.retain(|r| {
-                if expressions[r.index()].is_always_false() {
+                if matches!(expressions[r.index()].lhs, Expr::BoolConstant(false, ..)) {
                     state.set_dirty();
                     false
                 } else {
@@ -717,7 +724,7 @@ fn optimize_stmt(stmt: &mut Stmt, state: &mut OptimizerState, preserve_result: b
             });
 
             if let Some(index) = def_case {
-                optimize_expr(&mut expressions[*index].expr, state, false);
+                optimize_expr(&mut expressions[*index].rhs, state, false);
             }
 
             // Remove unused block statements
@@ -725,9 +732,9 @@ fn optimize_stmt(stmt: &mut Stmt, state: &mut OptimizerState, preserve_result: b
                 if *def_case != Some(index)
                     && cases.values().flat_map(|c| c.iter()).all(|&n| n != index)
                     && ranges.iter().all(|r| r.index() != index)
-                    && !b.expr.is_unit()
+                    && !b.rhs.is_unit()
                 {
-                    b.expr = Expr::Unit(b.expr.position());
+                    b.rhs = Expr::Unit(b.rhs.position());
                     state.set_dirty();
                 }
             });
@@ -1365,7 +1372,7 @@ pub fn optimize_into_ast(
     engine: &Engine,
     scope: Option<&Scope>,
     statements: StmtBlockContainer,
-    #[cfg(not(feature = "no_function"))] functions: Vec<crate::Shared<crate::ast::ScriptFnDef>>,
+    #[cfg(not(feature = "no_function"))] functions: Vec<crate::Shared<crate::ast::ScriptFuncDef>>,
     optimization_level: OptimizationLevel,
 ) -> AST {
     let mut statements = statements;
@@ -1384,7 +1391,7 @@ pub fn optimize_into_ast(
 
             functions
                 .iter()
-                .map(|fn_def| crate::ast::ScriptFnDef {
+                .map(|fn_def| crate::ast::ScriptFuncDef {
                     name: fn_def.name.clone(),
                     access: fn_def.access,
                     body: crate::ast::StmtBlock::NONE,
diff --git a/src/packages/array_basic.rs b/src/packages/array_basic.rs
index 7172c617b..f5d9ea93e 100644
--- a/src/packages/array_basic.rs
+++ b/src/packages/array_basic.rs
@@ -12,7 +12,6 @@ use crate::{
 #[cfg(feature = "no_std")]
 use std::prelude::v1::*;
 use std::{any::TypeId, cmp::Ordering, mem};
-use thin_vec::ThinVec;
 
 def_package! {
     /// Package of basic array utilities.
@@ -1272,7 +1271,7 @@ pub mod array_functions {
     pub fn dedup(ctx: NativeCallContext, array: &mut Array) {
         let comparer = FnPtr {
             name: ctx.engine().get_interned_string(OP_EQUALS),
-            curry: ThinVec::new(),
+            curry: <_>::default(),
             environ: None,
             #[cfg(not(feature = "no_function"))]
             fn_def: None,
diff --git a/src/packages/iter_basic.rs b/src/packages/iter_basic.rs
index 7e43705f1..a4f0417ae 100644
--- a/src/packages/iter_basic.rs
+++ b/src/packages/iter_basic.rs
@@ -244,6 +244,7 @@ macro_rules! reg_range {
             let _hash = $lib.set_native_fn($x, |from: $y, to: $y| Ok(from..to));
 
             #[cfg(feature = "metadata")]
+            #[allow(deprecated)]
             $lib.update_fn_metadata_with_comments(_hash, [
                     concat!("from: ", stringify!($y)),
                     concat!("to: ", stringify!($y)),
@@ -277,6 +278,7 @@ macro_rules! reg_range {
             let _hash = $lib.set_native_fn($x, |from: $y, to: $y, step: $y| StepRange::new(from, to, step, $add));
 
             #[cfg(feature = "metadata")]
+            #[allow(deprecated)]
             $lib.update_fn_metadata_with_comments(_hash, [
                     concat!("from: ", stringify!($y)),
                     concat!("to: ", stringify!($y)),
@@ -308,6 +310,7 @@ macro_rules! reg_range {
             let _hash = $lib.set_native_fn($x, |range: std::ops::Range<$y>, step: $y| StepRange::new(range.start, range.end, step, $add));
 
             #[cfg(feature = "metadata")]
+            #[allow(deprecated)]
             $lib.update_fn_metadata_with_comments(_hash, [
                     concat!("range: Range<", stringify!($y), ">"),
                     concat!("step: ", stringify!($y)),
@@ -385,6 +388,7 @@ def_package! {
             Ok(CharsStream::new(string, from, to - from))
         });
         #[cfg(feature = "metadata")]
+        #[allow(deprecated)]
         lib.update_fn_metadata_with_comments(
             _hash,
             ["string: &str", &range_type, "Iterator<char>"],
@@ -407,6 +411,7 @@ def_package! {
             Ok(CharsStream::new(string, from, to-from + 1))
         });
         #[cfg(feature = "metadata")]
+        #[allow(deprecated)]
         lib.update_fn_metadata_with_comments(
             _hash,
             ["string: &str", &range_inclusive_type, "Iterator<char>"],
@@ -425,6 +430,7 @@ def_package! {
 
         let _hash = lib.set_native_fn("chars", |string, from, len| Ok(CharsStream::new(string, from, len)));
         #[cfg(feature = "metadata")]
+        #[allow(deprecated)]
         lib.update_fn_metadata_with_comments(
             _hash,
             ["string: &str", "start: INT", "len: INT", "Iterator<char>"],
@@ -449,6 +455,7 @@ def_package! {
 
         let _hash = lib.set_native_fn("chars", |string, from| Ok(CharsStream::new(string, from, INT::MAX)));
         #[cfg(feature = "metadata")]
+        #[allow(deprecated)]
         lib.update_fn_metadata_with_comments(
             _hash,
             ["string: &str", "from: INT", "Iterator<char>"],
@@ -471,6 +478,7 @@ def_package! {
 
         let _hash = lib.set_native_fn("chars", |string| Ok(CharsStream::new(string, 0, INT::MAX)));
         #[cfg(feature = "metadata")]
+        #[allow(deprecated)]
         lib.update_fn_metadata_with_comments(
             _hash,
             ["string: &str", "Iterator<char>"],
@@ -491,6 +499,7 @@ def_package! {
         {
             let _hash = lib.set_getter_fn("chars", |string: &mut ImmutableString| Ok(CharsStream::new(string, 0, INT::MAX)));
             #[cfg(feature = "metadata")]
+            #[allow(deprecated)]
             lib.update_fn_metadata_with_comments(
                 _hash,
                 ["string: &mut ImmutableString", "Iterator<char>"],
@@ -517,6 +526,7 @@ def_package! {
             BitRange::new(value, from, to - from)
         });
         #[cfg(feature = "metadata")]
+        #[allow(deprecated)]
         lib.update_fn_metadata_with_comments(
             _hash,
             ["value: INT", &range_type, "Iterator<bool>"],
@@ -541,6 +551,7 @@ def_package! {
             BitRange::new(value, from, to - from + 1)
         });
         #[cfg(feature = "metadata")]
+        #[allow(deprecated)]
         lib.update_fn_metadata_with_comments(
             _hash,
             ["value: INT", &range_inclusive_type, "Iterator<bool>"],
@@ -561,6 +572,7 @@ def_package! {
 
         let _hash = lib.set_native_fn("bits", BitRange::new);
         #[cfg(feature = "metadata")]
+        #[allow(deprecated)]
         lib.update_fn_metadata_with_comments(
             _hash,
             ["value: INT", "from: INT", "len: INT", "Iterator<bool>"],
@@ -585,6 +597,7 @@ def_package! {
 
         let _hash = lib.set_native_fn("bits", |value, from| BitRange::new(value, from, INT::MAX));
         #[cfg(feature = "metadata")]
+        #[allow(deprecated)]
         lib.update_fn_metadata_with_comments(
             _hash,
             ["value: INT", "from: INT", "Iterator<bool>"],
@@ -607,6 +620,7 @@ def_package! {
 
         let _hash = lib.set_native_fn("bits", |value| BitRange::new(value, 0, INT::MAX) );
         #[cfg(feature = "metadata")]
+        #[allow(deprecated)]
         lib.update_fn_metadata_with_comments(
             _hash,
             ["value: INT", "Iterator<bool>"],
@@ -629,6 +643,7 @@ def_package! {
         {
             let _hash = lib.set_getter_fn("bits", |value: &mut INT| BitRange::new(*value, 0, INT::MAX) );
             #[cfg(feature = "metadata")]
+            #[allow(deprecated)]
             lib.update_fn_metadata_with_comments(
                 _hash,
                 ["value: &mut INT", "Iterator<bool>"],
diff --git a/src/packages/lang_core.rs b/src/packages/lang_core.rs
index 8f1ded8ce..1efc688cc 100644
--- a/src/packages/lang_core.rs
+++ b/src/packages/lang_core.rs
@@ -32,7 +32,7 @@ mod core_functions {
     /// ```rhai
     /// exit(42);
     /// ```
-    #[rhai_fn(name = "exit", return_raw)]
+    #[rhai_fn(name = "exit", volatile, return_raw)]
     pub fn exit_with_value(value: Dynamic) -> RhaiResult {
         Err(ERR::Exit(value, Position::NONE).into())
     }
@@ -42,7 +42,7 @@ mod core_functions {
     /// ```rhai
     /// exit();
     /// ```
-    #[rhai_fn(return_raw)]
+    #[rhai_fn(volatile, return_raw)]
     pub fn exit() -> RhaiResult {
         Err(ERR::Exit(Dynamic::UNIT, Position::NONE).into())
     }
@@ -134,9 +134,9 @@ mod core_functions {
     /// ```
     #[cfg(not(feature = "no_float"))]
     #[cfg(not(feature = "no_std"))]
-    #[rhai_fn(name = "sleep")]
+    #[rhai_fn(name = "sleep", volatile)]
     pub fn sleep_float(seconds: FLOAT) {
-        if seconds <= 0.0 {
+        if !seconds.is_normal() || seconds.is_sign_negative() {
             return;
         }
 
@@ -154,6 +154,7 @@ mod core_functions {
     /// sleep(10);
     /// ```
     #[cfg(not(feature = "no_std"))]
+    #[rhai_fn(volatile)]
     pub fn sleep(seconds: INT) {
         if seconds <= 0 {
             return;
@@ -216,18 +217,18 @@ mod reflection_functions {
 #[cfg(not(feature = "no_object"))]
 fn collect_fn_metadata(
     ctx: &NativeCallContext,
-    filter: impl Fn(FnNamespace, FnAccess, &str, usize, &crate::Shared<crate::ast::ScriptFnDef>) -> bool
+    filter: impl Fn(FnNamespace, FnAccess, &str, usize, &crate::Shared<crate::ast::ScriptFuncDef>) -> bool
         + Copy,
 ) -> crate::Array {
     #[cfg(not(feature = "no_module"))]
     use crate::Identifier;
-    use crate::{ast::ScriptFnDef, engine::FN_ANONYMOUS, Array, Map};
+    use crate::{ast::ScriptFuncDef, engine::FN_ANONYMOUS, Array, Map};
 
     // Create a metadata record for a function.
     fn make_metadata(
         engine: &Engine,
         #[cfg(not(feature = "no_module"))] namespace: Identifier,
-        func: &ScriptFnDef,
+        func: &ScriptFuncDef,
     ) -> Map {
         let mut map = Map::new();
 
@@ -346,7 +347,7 @@ fn collect_fn_metadata(
             list: &mut Array,
             namespace: &str,
             module: &Module,
-            filter: impl Fn(FnNamespace, FnAccess, &str, usize, &Shared<ScriptFnDef>) -> bool + Copy,
+            filter: impl Fn(FnNamespace, FnAccess, &str, usize, &Shared<ScriptFuncDef>) -> bool + Copy,
         ) {
             module
                 .iter_script_fn()
diff --git a/src/packages/math_basic.rs b/src/packages/math_basic.rs
index 3f427f0b8..06f1d93c7 100644
--- a/src/packages/math_basic.rs
+++ b/src/packages/math_basic.rs
@@ -377,13 +377,13 @@ mod decimal_functions {
     /// Return the natural number _e_.
     #[cfg(feature = "no_float")]
     #[rhai_fn(name = "PI")]
-    pub fn pi() -> Decimal {
+    pub const fn pi() -> Decimal {
         Decimal::PI
     }
     /// Return the number π.
     #[cfg(feature = "no_float")]
     #[rhai_fn(name = "E")]
-    pub fn e() -> Decimal {
+    pub const fn e() -> Decimal {
         Decimal::E
     }
     /// Parse a string into a decimal number.
diff --git a/src/parser.rs b/src/parser.rs
index 56c7146fb..0d6559427 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -2,9 +2,9 @@
 
 use crate::api::options::LangOptions;
 use crate::ast::{
-    ASTFlags, BinaryExpr, CaseBlocksList, ConditionalExpr, Expr, FlowControl, FnCallExpr,
-    FnCallHashes, Ident, Namespace, OpAssignment, RangeCase, ScriptFnDef, Stmt, StmtBlock,
-    StmtBlockContainer, SwitchCasesCollection,
+    ASTFlags, BinaryExpr, CaseBlocksList, Expr, FlowControl, FnCallExpr, FnCallHashes, Ident,
+    Namespace, OpAssignment, RangeCase, ScriptFuncDef, Stmt, StmtBlock, StmtBlockContainer,
+    SwitchCasesCollection,
 };
 use crate::engine::{Precedence, OP_CONTAINS, OP_NOT};
 use crate::eval::{Caches, GlobalRuntimeState};
@@ -35,7 +35,7 @@ use thin_vec::ThinVec;
 
 pub type ParseResult<T> = Result<T, ParseError>;
 
-type FnLib = StraightHashMap<Shared<ScriptFnDef>>;
+type FnLib = StraightHashMap<Shared<ScriptFuncDef>>;
 
 /// Invalid variable name that acts as a search barrier in a [`Scope`].
 const SCOPE_SEARCH_BARRIER_MARKER: &str = "$ BARRIER $";
@@ -639,7 +639,7 @@ impl Engine {
         };
 
         let mut _namespace = namespace;
-        let mut args = Vec::new();
+        let mut args = FnArgsVec::new();
 
         match token {
             // id( <EOF>
@@ -702,7 +702,7 @@ impl Engine {
                     op_token: None,
                     namespace: _namespace,
                     hashes,
-                    args: args.into_boxed_slice(),
+                    args,
                 }
                 .into_fn_call_expr(settings.pos));
             }
@@ -769,7 +769,7 @@ impl Engine {
                         op_token: None,
                         namespace: _namespace,
                         hashes,
-                        args: args.into_boxed_slice(),
+                        args,
                     }
                     .into_fn_call_expr(settings.pos));
                 }
@@ -1164,9 +1164,9 @@ impl Engine {
             }
         }
 
-        let mut expressions = ThinVec::<ConditionalExpr>::new();
+        let mut expressions = FnArgsVec::<BinaryExpr>::new();
         let mut cases = StraightHashMap::<CaseBlocksList>::default();
-        let mut ranges = ThinVec::<RangeCase>::new();
+        let mut ranges = StaticVec::<RangeCase>::new();
         let mut def_case = None;
         let mut def_case_pos = Position::NONE;
 
@@ -1261,7 +1261,11 @@ impl Engine {
                     (Expr::Stmt(stmt_block.into()), need_comma)
                 };
 
-            expressions.push((condition, action_expr).into());
+            expressions.push(BinaryExpr {
+                lhs: condition,
+                rhs: action_expr,
+            });
+
             let index = expressions.len() - 1;
 
             if case_expr_list.is_empty() {
@@ -1282,14 +1286,11 @@ impl Engine {
 
                     if let Some(mut r) = range_value {
                         if !r.is_empty() {
-                            // Other range
                             r.set_index(index);
                             ranges.push(r);
                         }
-                        continue;
-                    }
-
-                    if !ranges.is_empty() {
+                    } else if !ranges.is_empty() {
+                        // Check for numeric values after ranges
                         let forbidden = match value {
                             Dynamic(Union::Int(..)) => true,
                             #[cfg(not(feature = "no_float"))]
@@ -1470,6 +1471,14 @@ impl Engine {
 
             // | ...
             #[cfg(not(feature = "no_function"))]
+            #[cfg(not(feature = "unchecked"))]
+            Token::Pipe | Token::Or
+                if settings.has_option(LangOptions::ANON_FN)
+                    && lib.len() >= self.max_functions() =>
+            {
+                return Err(PERR::TooManyFunctions.into_err(settings.pos));
+            }
+            #[cfg(not(feature = "no_function"))]
             Token::Pipe | Token::Or if settings.has_option(LangOptions::ANON_FN) => {
                 // Build new parse state
                 let new_interner = &mut StringsInterner::new();
@@ -1990,7 +1999,7 @@ impl Engine {
                         namespace: Namespace::NONE,
                         name: state.get_interned_string("-"),
                         hashes: FnCallHashes::from_native_only(calc_fn_hash(None, "-", 1)),
-                        args: vec![expr].into_boxed_slice(),
+                        args: IntoIterator::into_iter([expr]).collect(),
                         op_token: Some(token),
                         capture_parent_scope: false,
                     }
@@ -2012,7 +2021,7 @@ impl Engine {
                         namespace: Namespace::NONE,
                         name: state.get_interned_string("+"),
                         hashes: FnCallHashes::from_native_only(calc_fn_hash(None, "+", 1)),
-                        args: vec![expr].into_boxed_slice(),
+                        args: IntoIterator::into_iter([expr]).collect(),
                         op_token: Some(token),
                         capture_parent_scope: false,
                     }
@@ -2028,8 +2037,10 @@ impl Engine {
                     namespace: Namespace::NONE,
                     name: state.get_interned_string("!"),
                     hashes: FnCallHashes::from_native_only(calc_fn_hash(None, "!", 1)),
-                    args: vec![self.parse_unary(input, state, lib, settings.level_up()?)?]
-                        .into_boxed_slice(),
+                    args: {
+                        let expr = self.parse_unary(input, state, lib, settings.level_up()?)?;
+                        IntoIterator::into_iter([expr]).collect()
+                    },
                     op_token: Some(token),
                     capture_parent_scope: false,
                 }
@@ -2387,7 +2398,7 @@ impl Engine {
                 namespace: Namespace::NONE,
                 name: state.get_interned_string(&op),
                 hashes: FnCallHashes::from_native_only(hash),
-                args: vec![root, rhs].into_boxed_slice(),
+                args: IntoIterator::into_iter([root, rhs]).collect(),
                 op_token: native_only.then(|| op_token.clone()),
                 capture_parent_scope: false,
             };
@@ -2440,7 +2451,7 @@ impl Engine {
                             namespace: Namespace::NONE,
                             name: state.get_interned_string(OP_NOT),
                             hashes: FnCallHashes::from_native_only(calc_fn_hash(None, OP_NOT, 1)),
-                            args: vec![fn_call].into_boxed_slice(),
+                            args: IntoIterator::into_iter([fn_call]).collect(),
                             op_token: Some(Token::Bang),
                             capture_parent_scope: false,
                         };
@@ -2485,9 +2496,9 @@ impl Engine {
 
         let pos = settings.pos;
 
-        let mut inputs = Vec::new();
-        let mut segments = Vec::new();
-        let mut tokens = Vec::new();
+        let mut inputs = FnArgsVec::new();
+        let mut segments = FnArgsVec::new();
+        let mut tokens = FnArgsVec::new();
 
         // Adjust the variables stack
         if syntax.scope_may_be_changed {
@@ -2655,8 +2666,8 @@ impl Engine {
 
         Ok(Expr::Custom(
             crate::ast::CustomExpr {
-                inputs: inputs.into_boxed_slice(),
-                tokens: tokens.into_boxed_slice(),
+                inputs,
+                tokens,
                 state: user_state,
                 scope_may_be_changed: syntax.scope_may_be_changed,
                 self_terminated,
@@ -3343,6 +3354,10 @@ impl Engine {
                 };
 
                 match input.next().unwrap() {
+                    #[cfg(not(feature = "unchecked"))]
+                    (Token::Fn, pos) if lib.len() >= self.max_functions() => {
+                        Err(PERR::TooManyFunctions.into_err(pos))
+                    }
                     (Token::Fn, pos) => {
                         // Build new parse state
                         let new_state = &mut ParseState::new(
@@ -3597,7 +3612,7 @@ impl Engine {
         settings: ParseSettings,
         access: crate::FnAccess,
         #[cfg(feature = "metadata")] comments: impl IntoIterator<Item = crate::Identifier>,
-    ) -> ParseResult<ScriptFnDef> {
+    ) -> ParseResult<ScriptFuncDef> {
         let settings = settings.level_up()?;
 
         let (token, pos) = input.next().unwrap();
@@ -3709,7 +3724,7 @@ impl Engine {
         let mut params: FnArgsVec<_> = params.into_iter().map(|(p, ..)| p).collect();
         params.shrink_to_fit();
 
-        Ok(ScriptFnDef {
+        Ok(ScriptFuncDef {
             name: state.get_interned_string(name),
             access,
             #[cfg(not(feature = "no_object"))]
@@ -3738,7 +3753,7 @@ impl Engine {
         }
 
         let num_externals = externals.as_ref().len();
-        let mut args = Vec::with_capacity(externals.as_ref().len() + 1);
+        let mut args = FnArgsVec::with_capacity(externals.as_ref().len() + 1);
 
         args.push(fn_expr);
 
@@ -3765,7 +3780,7 @@ impl Engine {
                 crate::engine::KEYWORD_FN_PTR_CURRY,
                 num_externals + 1,
             )),
-            args: args.into_boxed_slice(),
+            args,
             op_token: None,
             capture_parent_scope: false,
         }
@@ -3797,7 +3812,7 @@ impl Engine {
         lib: &mut FnLib,
         settings: ParseSettings,
         _parent: &mut ParseState,
-    ) -> ParseResult<(Expr, Shared<ScriptFnDef>)> {
+    ) -> ParseResult<(Expr, Shared<ScriptFuncDef>)> {
         use core::iter::FromIterator;
 
         let settings = settings.level_up()?;
@@ -3875,7 +3890,7 @@ impl Engine {
         let fn_name = state.get_interned_string(make_anonymous_fn(hash));
 
         // Define the function
-        let script = Shared::new(ScriptFnDef {
+        let script = Shared::new(ScriptFuncDef {
             name: fn_name.clone(),
             access: crate::FnAccess::Public,
             #[cfg(not(feature = "no_object"))]
@@ -3964,7 +3979,7 @@ impl Engine {
         mut input: TokenStream,
         state: &mut ParseState,
         process_settings: impl FnOnce(&mut ParseSettings),
-    ) -> ParseResult<(StmtBlockContainer, Vec<Shared<ScriptFnDef>>)> {
+    ) -> ParseResult<(StmtBlockContainer, Vec<Shared<ScriptFuncDef>>)> {
         let mut statements = StmtBlockContainer::new_const();
         let mut functions = <_>::default();
 
diff --git a/src/serde/metadata.rs b/src/serde/metadata.rs
index 60def14b2..3dfd3fbe5 100644
--- a/src/serde/metadata.rs
+++ b/src/serde/metadata.rs
@@ -2,7 +2,8 @@
 #![cfg(feature = "metadata")]
 
 use crate::api::formatting::format_type;
-use crate::module::{calc_native_fn_hash, FuncInfo, ModuleFlags};
+use crate::func::RhaiFunc;
+use crate::module::{calc_native_fn_hash, FuncMetadata, ModuleFlags};
 use crate::types::custom_types::CustomTypeInfo;
 use crate::{calc_fn_hash, Engine, FnAccess, SmartString, AST};
 use serde::{Deserialize, Serialize};
@@ -102,15 +103,29 @@ impl Ord for FnMetadata<'_> {
     }
 }
 
-impl<'a> From<&'a FuncInfo> for FnMetadata<'a> {
-    fn from(info: &'a FuncInfo) -> Self {
-        let base_hash = calc_fn_hash(None, &info.metadata.name, info.metadata.num_params);
-        let (typ, full_hash) = if info.func.is_script() {
-            (FnType::Script, base_hash)
+impl<'a> From<(&'a RhaiFunc, &'a FuncMetadata)> for FnMetadata<'a> {
+    fn from(info: (&'a RhaiFunc, &'a FuncMetadata)) -> Self {
+        let (f, m) = info;
+        let base_hash = calc_fn_hash(None, &m.name, m.num_params);
+        let (typ, full_hash, _this_type) = if f.is_script() {
+            (
+                FnType::Script,
+                base_hash,
+                #[cfg(not(feature = "no_function"))]
+                #[cfg(not(feature = "no_object"))]
+                f.get_script_fn_def()
+                    .unwrap()
+                    .this_type
+                    .as_ref()
+                    .map(|s| s.as_str()),
+                #[cfg(any(feature = "no_object", feature = "no_function"))]
+                None::<&str>,
+            )
         } else {
             (
                 FnType::Native,
-                calc_native_fn_hash(None, &info.metadata.name, &info.metadata.param_types),
+                calc_native_fn_hash(None, &m.name, &m.param_types),
+                None::<&str>,
             )
         };
 
@@ -118,17 +133,16 @@ impl<'a> From<&'a FuncInfo> for FnMetadata<'a> {
             base_hash,
             full_hash,
             #[cfg(not(feature = "no_module"))]
-            namespace: info.metadata.namespace,
-            access: info.metadata.access,
-            name: &info.metadata.name,
+            namespace: m.namespace,
+            access: m.access,
+            name: &m.name,
             #[cfg(not(feature = "no_function"))]
-            is_anonymous: crate::parser::is_anonymous_fn(&info.metadata.name),
+            is_anonymous: crate::parser::is_anonymous_fn(&m.name),
             typ,
             #[cfg(not(feature = "no_object"))]
-            this_type: info.metadata.this_type.as_deref(),
-            num_params: info.metadata.num_params,
-            params: info
-                .metadata
+            this_type: _this_type,
+            num_params: m.num_params,
+            params: m
                 .params_info
                 .iter()
                 .map(|s| {
@@ -141,22 +155,21 @@ impl<'a> From<&'a FuncInfo> for FnMetadata<'a> {
                     FnParam { name, typ }
                 })
                 .collect(),
-            return_type: format_type(&info.metadata.return_type, true),
-            signature: info.gen_signature().into(),
-            doc_comments: if info.func.is_script() {
+            return_type: format_type(&m.return_type, true),
+            signature: m.gen_signature().into(),
+            doc_comments: if f.is_script() {
                 #[cfg(feature = "no_function")]
                 unreachable!("script-defined functions should not exist under no_function");
 
                 #[cfg(not(feature = "no_function"))]
-                info.func
-                    .get_script_fn_def()
-                    .expect("`ScriptFnDef`")
+                f.get_script_fn_def()
+                    .expect("`ScriptFuncDef`")
                     .comments
                     .iter()
                     .map(<_>::as_ref)
                     .collect()
             } else {
-                info.metadata.comments.iter().map(<_>::as_ref).collect()
+                m.comments.iter().map(<_>::as_ref).collect()
             },
         }
     }
diff --git a/src/serde/ser.rs b/src/serde/ser.rs
index 14cc2fee7..c4030dbde 100644
--- a/src/serde/ser.rs
+++ b/src/serde/ser.rs
@@ -17,7 +17,7 @@ pub struct DynamicSerializer {
     /// Buffer to hold a temporary key.
     _key: Identifier,
     /// Buffer to hold a temporary value.
-    value: Dynamic,
+    _value: Dynamic,
 }
 
 impl DynamicSerializer {
@@ -26,7 +26,7 @@ impl DynamicSerializer {
     pub const fn new(value: Dynamic) -> Self {
         Self {
             _key: Identifier::new_const(),
-            value,
+            _value: value,
         }
     }
 }
@@ -464,7 +464,7 @@ impl SerializeSeq for DynamicSerializer {
         #[cfg(not(feature = "no_index"))]
         {
             let value = _value.serialize(&mut *self)?;
-            let arr = self.value.downcast_mut::<crate::Array>().unwrap();
+            let arr = self._value.downcast_mut::<crate::Array>().unwrap();
             arr.push(value);
             Ok(())
         }
@@ -481,7 +481,7 @@ impl SerializeSeq for DynamicSerializer {
     #[inline]
     fn end(self) -> RhaiResultOf<Self::Ok> {
         #[cfg(not(feature = "no_index"))]
-        return Ok(self.value);
+        return Ok(self._value);
         #[cfg(feature = "no_index")]
         return Err(ERR::ErrorMismatchDataType(
             "".into(),
@@ -500,7 +500,7 @@ impl SerializeTuple for DynamicSerializer {
         #[cfg(not(feature = "no_index"))]
         {
             let value = _value.serialize(&mut *self)?;
-            let arr = self.value.downcast_mut::<crate::Array>().unwrap();
+            let arr = self._value.downcast_mut::<crate::Array>().unwrap();
             arr.push(value);
             Ok(())
         }
@@ -516,7 +516,7 @@ impl SerializeTuple for DynamicSerializer {
     #[inline]
     fn end(self) -> RhaiResultOf<Self::Ok> {
         #[cfg(not(feature = "no_index"))]
-        return Ok(self.value);
+        return Ok(self._value);
         #[cfg(feature = "no_index")]
         return Err(ERR::ErrorMismatchDataType(
             "".into(),
@@ -535,7 +535,7 @@ impl SerializeTupleStruct for DynamicSerializer {
         #[cfg(not(feature = "no_index"))]
         {
             let value = _value.serialize(&mut *self)?;
-            let arr = self.value.downcast_mut::<crate::Array>().unwrap();
+            let arr = self._value.downcast_mut::<crate::Array>().unwrap();
             arr.push(value);
             Ok(())
         }
@@ -551,7 +551,7 @@ impl SerializeTupleStruct for DynamicSerializer {
     #[inline]
     fn end(self) -> RhaiResultOf<Self::Ok> {
         #[cfg(not(feature = "no_index"))]
-        return Ok(self.value);
+        return Ok(self._value);
         #[cfg(feature = "no_index")]
         return Err(ERR::ErrorMismatchDataType(
             "".into(),
@@ -592,7 +592,7 @@ impl SerializeMap for DynamicSerializer {
         {
             let key = std::mem::take(&mut self._key);
             let value = _value.serialize(&mut *self)?;
-            let map = self.value.downcast_mut::<crate::Map>().unwrap();
+            let map = self._value.downcast_mut::<crate::Map>().unwrap();
             map.insert(key, value);
             Ok(())
         }
@@ -617,7 +617,7 @@ impl SerializeMap for DynamicSerializer {
                 ERR::ErrorMismatchDataType("string".into(), typ.into(), Position::NONE)
             })?;
             let value = _value.serialize(&mut *self)?;
-            let map = self.value.downcast_mut::<crate::Map>().unwrap();
+            let map = self._value.downcast_mut::<crate::Map>().unwrap();
             map.insert(key.into(), value);
             Ok(())
         }
@@ -633,7 +633,7 @@ impl SerializeMap for DynamicSerializer {
     #[inline]
     fn end(self) -> RhaiResultOf<Self::Ok> {
         #[cfg(not(feature = "no_object"))]
-        return Ok(self.value);
+        return Ok(self._value);
         #[cfg(feature = "no_object")]
         return Err(ERR::ErrorMismatchDataType(
             "".into(),
@@ -656,7 +656,7 @@ impl SerializeStruct for DynamicSerializer {
         #[cfg(not(feature = "no_object"))]
         {
             let value = _value.serialize(&mut *self)?;
-            let map = self.value.downcast_mut::<crate::Map>().unwrap();
+            let map = self._value.downcast_mut::<crate::Map>().unwrap();
             map.insert(_key.into(), value);
             Ok(())
         }
@@ -672,7 +672,7 @@ impl SerializeStruct for DynamicSerializer {
     #[inline]
     fn end(self) -> RhaiResultOf<Self::Ok> {
         #[cfg(not(feature = "no_object"))]
-        return Ok(self.value);
+        return Ok(self._value);
         #[cfg(feature = "no_object")]
         return Err(ERR::ErrorMismatchDataType(
             "".into(),
diff --git a/src/tests.rs b/src/tests.rs
index 56871ec22..d4b3550e4 100644
--- a/src/tests.rs
+++ b/src/tests.rs
@@ -31,10 +31,7 @@ fn check_struct_sizes() {
     );
 
     #[cfg(feature = "internals")]
-    {
-        assert_eq!(size_of::<CallableFunction>(), 3 * WORD_SIZE);
-        assert_eq!(size_of::<module::FuncInfo>(), 4 * WORD_SIZE);
-    }
+    assert_eq!(size_of::<RhaiFunc>(), 3 * WORD_SIZE);
 
     // The following only on 64-bit platforms
 
diff --git a/src/tokenizer.rs b/src/tokenizer.rs
index f2c380e4f..191fb6d12 100644
--- a/src/tokenizer.rs
+++ b/src/tokenizer.rs
@@ -2,7 +2,7 @@
 
 use crate::engine::Precedence;
 use crate::func::native::OnParseTokenCallback;
-use crate::{Engine, Identifier, LexError, Position, SmartString, INT, UNSIGNED_INT};
+use crate::{Engine, Identifier, LexError, Position, SmartString, StaticVec, INT, UNSIGNED_INT};
 #[cfg(feature = "no_std")]
 use std::prelude::v1::*;
 use std::{
@@ -2398,10 +2398,8 @@ pub struct MultiInputsStream<'a> {
     pub buf: [Option<char>; 2],
     /// The current stream index.
     pub index: usize,
-    /// The first input character stream.
-    pub stream: Peekable<Chars<'a>>,
-    /// Extra input character streams.
-    pub extra_streams: Box<[Peekable<Chars<'a>>]>,
+    /// Input character streams.
+    pub streams: StaticVec<Peekable<Chars<'a>>>,
 }
 
 impl InputStream for MultiInputsStream<'_> {
@@ -2427,17 +2425,12 @@ impl InputStream for MultiInputsStream<'_> {
         }
 
         loop {
-            if self.index > self.extra_streams.len() {
+            if self.index >= self.streams.len() {
                 // No more streams
                 return None;
             }
-            if self.index == 0 {
-                if let Some(ch) = self.stream.next() {
-                    // Next character in main stream
-                    return Some(ch);
-                }
-            } else if let Some(ch) = self.extra_streams[self.index - 1].next() {
-                // Next character in current stream
+            if let Some(ch) = self.streams[self.index].next() {
+                // Next character in main stream
                 return Some(ch);
             }
             // Jump to the next stream
@@ -2452,17 +2445,12 @@ impl InputStream for MultiInputsStream<'_> {
         }
 
         loop {
-            if self.index > self.extra_streams.len() {
+            if self.index >= self.streams.len() {
                 // No more streams
                 return None;
             }
-            if self.index == 0 {
-                if let Some(&ch) = self.stream.peek() {
-                    // Next character in main stream
-                    return Some(ch);
-                }
-            } else if let Some(&ch) = self.extra_streams[self.index - 1].peek() {
-                // Next character in current stream
+            if let Some(&ch) = self.streams[self.index].peek() {
+                // Next character in main stream
                 return Some(ch);
             }
             // Jump to the next stream
@@ -2689,8 +2677,6 @@ pub fn lex_raw<'a>(
     let buffer: TokenizerControl = RefCell::new(TokenizerControlBlock::new()).into();
     let buffer2 = buffer.clone();
 
-    let mut input_streams = inputs.into_iter().map(|s| s.as_ref().chars().peekable());
-
     (
         TokenIterator {
             engine,
@@ -2707,8 +2693,10 @@ pub fn lex_raw<'a>(
             pos: Position::new(1, 0),
             stream: MultiInputsStream {
                 buf: [None, None],
-                stream: input_streams.next().unwrap(),
-                extra_streams: input_streams.collect(),
+                streams: inputs
+                    .into_iter()
+                    .map(|s| s.as_ref().chars().peekable())
+                    .collect(),
                 index: 0,
             },
             token_mapper,
diff --git a/src/types/custom_types.rs b/src/types/custom_types.rs
index 3419fbb39..a9819a71a 100644
--- a/src/types/custom_types.rs
+++ b/src/types/custom_types.rs
@@ -26,7 +26,7 @@ pub struct CustomTypeInfo {
     ///
     /// Each line in non-block doc-comments starts with `///`.
     #[cfg(feature = "metadata")]
-    pub comments: Box<[crate::SmartString]>,
+    pub comments: crate::StaticVec<crate::SmartString>,
 }
 
 /// _(internals)_ A collection of custom types.
diff --git a/src/types/dynamic.rs b/src/types/dynamic.rs
index 4ffdacf43..f45f98dc0 100644
--- a/src/types/dynamic.rs
+++ b/src/types/dynamic.rs
@@ -400,15 +400,71 @@ impl Hash for Dynamic {
             Union::Blob(ref a, ..) => a.hash(state),
             #[cfg(not(feature = "no_object"))]
             Union::Map(ref m, ..) => m.hash(state),
-            Union::FnPtr(ref f, ..) => f.hash(state),
+            Union::FnPtr(ref f, ..) if f.environ.is_some() => {
+                unimplemented!("FnPtr with embedded environment cannot be hashed")
+            }
+            Union::FnPtr(ref f, ..) => {
+                f.fn_name().hash(state);
+                f.curry().hash(state);
+            }
 
             #[cfg(not(feature = "no_closure"))]
             Union::Shared(ref cell, ..) => (*crate::func::locked_read(cell)).hash(state),
 
-            Union::Variant(..) => unimplemented!("{} cannot be hashed", self.type_name()),
+            Union::Variant(ref v, ..) => {
+                let _value_any = (***v).as_any();
+
+                #[cfg(not(feature = "only_i32"))]
+                #[cfg(not(feature = "only_i64"))]
+                if let Some(value) = _value_any.downcast_ref::<u8>() {
+                    return value.hash(state);
+                } else if let Some(value) = _value_any.downcast_ref::<u16>() {
+                    return value.hash(state);
+                } else if let Some(value) = _value_any.downcast_ref::<u32>() {
+                    return value.hash(state);
+                } else if let Some(value) = _value_any.downcast_ref::<u64>() {
+                    return value.hash(state);
+                } else if let Some(value) = _value_any.downcast_ref::<i8>() {
+                    return value.hash(state);
+                } else if let Some(value) = _value_any.downcast_ref::<i16>() {
+                    return value.hash(state);
+                } else if let Some(value) = _value_any.downcast_ref::<i32>() {
+                    return value.hash(state);
+                } else if let Some(value) = _value_any.downcast_ref::<i64>() {
+                    return value.hash(state);
+                }
+
+                #[cfg(not(feature = "no_float"))]
+                #[cfg(not(feature = "f32_float"))]
+                if let Some(value) = _value_any.downcast_ref::<f32>() {
+                    return value.to_ne_bytes().hash(state);
+                }
+                #[cfg(not(feature = "no_float"))]
+                #[cfg(feature = "f32_float")]
+                if let Some(value) = _value_any.downcast_ref::<f64>() {
+                    return value.to_ne_bytes().hash(state);
+                }
+
+                #[cfg(not(feature = "only_i32"))]
+                #[cfg(not(feature = "only_i64"))]
+                #[cfg(not(target_family = "wasm"))]
+                if let Some(value) = _value_any.downcast_ref::<u128>() {
+                    return value.hash(state);
+                } else if let Some(value) = _value_any.downcast_ref::<i128>() {
+                    return value.hash(state);
+                }
+
+                if let Some(range) = _value_any.downcast_ref::<ExclusiveRange>() {
+                    return range.hash(state);
+                } else if let Some(range) = _value_any.downcast_ref::<InclusiveRange>() {
+                    return range.hash(state);
+                }
+
+                unimplemented!("Custom type {} cannot be hashed", self.type_name())
+            }
 
             #[cfg(not(feature = "no_time"))]
-            Union::TimeStamp(..) => unimplemented!("{} cannot be hashed", self.type_name()),
+            Union::TimeStamp(..) => unimplemented!("Timestamp cannot be hashed"),
         }
     }
 }
@@ -1153,15 +1209,67 @@ impl Dynamic {
 
             #[cfg(not(feature = "no_float"))]
             Union::Float(..) => true,
+            #[cfg(feature = "decimal")]
+            Union::Decimal(..) => true,
             #[cfg(not(feature = "no_index"))]
-            Union::Array(..) => true,
+            Union::Array(ref a, ..) => a.iter().all(Self::is_hashable),
+            #[cfg(not(feature = "no_index"))]
+            Union::Blob(..) => true,
             #[cfg(not(feature = "no_object"))]
-            Union::Map(..) => true,
+            Union::Map(ref m, ..) => m.values().all(Self::is_hashable),
+            Union::FnPtr(ref f, ..) => {
+                f.environ.is_none() && f.curry().iter().all(Self::is_hashable)
+            }
+            #[cfg(not(feature = "no_time"))]
+            Union::TimeStamp(..) => false,
+
+            Union::Variant(ref v, ..) => {
+                let _value_any = (***v).as_any();
+                let _type_id = _value_any.type_id();
+
+                #[cfg(not(feature = "only_i32"))]
+                #[cfg(not(feature = "only_i64"))]
+                if _type_id == TypeId::of::<u8>()
+                    || _type_id == TypeId::of::<u16>()
+                    || _type_id == TypeId::of::<u32>()
+                    || _type_id == TypeId::of::<u64>()
+                    || _type_id == TypeId::of::<i8>()
+                    || _type_id == TypeId::of::<i16>()
+                    || _type_id == TypeId::of::<i32>()
+                    || _type_id == TypeId::of::<i64>()
+                {
+                    return true;
+                }
+
+                #[cfg(not(feature = "no_float"))]
+                #[cfg(not(feature = "f32_float"))]
+                if _type_id == TypeId::of::<f32>() {
+                    return true;
+                }
+                #[cfg(not(feature = "no_float"))]
+                #[cfg(feature = "f32_float")]
+                if _type_id == TypeId::of::<f64>() {
+                    return true;
+                }
+
+                #[cfg(not(feature = "only_i32"))]
+                #[cfg(not(feature = "only_i64"))]
+                #[cfg(not(target_family = "wasm"))]
+                if _type_id == TypeId::of::<u128>() || _type_id == TypeId::of::<i128>() {
+                    return true;
+                }
+
+                if _type_id == TypeId::of::<ExclusiveRange>()
+                    || _type_id == TypeId::of::<InclusiveRange>()
+                {
+                    return true;
+                }
+
+                false
+            }
 
             #[cfg(not(feature = "no_closure"))]
             Union::Shared(ref cell, ..) => crate::func::locked_read(cell).is_hashable(),
-
-            _ => false,
         }
     }
     /// Create a [`Dynamic`] from any type.  A [`Dynamic`] value is simply returned as is.
@@ -1540,7 +1648,7 @@ impl Dynamic {
     pub fn flatten(self) -> Self {
         match self.0 {
             #[cfg(not(feature = "no_closure"))]
-            Union::Shared(cell, ..) => crate::func::shared_try_take(cell).map_or_else(
+            Union::Shared(cell, ..) => crate::func::native::shared_try_take(cell).map_or_else(
                 |ref cell| crate::func::locked_read(cell).clone(),
                 #[cfg(not(feature = "sync"))]
                 crate::Locked::into_inner,
diff --git a/src/types/fn_ptr.rs b/src/types/fn_ptr.rs
index 57d439254..679ee6817 100644
--- a/src/types/fn_ptr.rs
+++ b/src/types/fn_ptr.rs
@@ -1,7 +1,7 @@
 //! The `FnPtr` type.
 
+use crate::ast::EncapsulatedEnviron;
 use crate::eval::GlobalRuntimeState;
-use crate::func::EncapsulatedEnviron;
 use crate::tokenizer::{is_reserved_keyword_or_symbol, is_valid_function_name, Token};
 use crate::types::dynamic::Variant;
 use crate::{
@@ -13,9 +13,7 @@ use std::prelude::v1::*;
 use std::{
     any::type_name,
     convert::{TryFrom, TryInto},
-    fmt,
-    hash::{Hash, Hasher},
-    mem,
+    fmt, mem,
     ops::{Index, IndexMut},
 };
 use thin_vec::ThinVec;
@@ -28,22 +26,7 @@ pub struct FnPtr {
     pub(crate) curry: ThinVec<Dynamic>,
     pub(crate) environ: Option<Shared<EncapsulatedEnviron>>,
     #[cfg(not(feature = "no_function"))]
-    pub(crate) fn_def: Option<Shared<crate::ast::ScriptFnDef>>,
-}
-
-impl Hash for FnPtr {
-    #[inline(always)]
-    fn hash<H: Hasher>(&self, state: &mut H) {
-        self.name.hash(state);
-        self.curry.hash(state);
-
-        // Hash the shared [`EncapsulatedEnviron`] by hashing its shared pointer.
-        self.environ.as_ref().map(Shared::as_ptr).hash(state);
-
-        // Hash the linked [`ScriptFnDef`][crate::ast::ScriptFnDef] by hashing its shared pointer.
-        #[cfg(not(feature = "no_function"))]
-        self.fn_def.as_ref().map(Shared::as_ptr).hash(state);
-    }
+    pub(crate) fn_def: Option<Shared<crate::ast::ScriptFuncDef>>,
 }
 
 impl fmt::Display for FnPtr {
@@ -486,7 +469,7 @@ impl TryFrom<ImmutableString> for FnPtr {
 }
 
 #[cfg(not(feature = "no_function"))]
-impl<T: Into<Shared<crate::ast::ScriptFnDef>>> From<T> for FnPtr {
+impl<T: Into<Shared<crate::ast::ScriptFuncDef>>> From<T> for FnPtr {
     #[inline(always)]
     fn from(value: T) -> Self {
         let fn_def = value.into();
diff --git a/src/types/parse_error.rs b/src/types/parse_error.rs
index 7ddd0db35..a735372bf 100644
--- a/src/types/parse_error.rs
+++ b/src/types/parse_error.rs
@@ -177,6 +177,8 @@ pub enum ParseErrorType {
     ModuleUndefined(String),
     /// Expression exceeding the maximum levels of complexity.
     ExprTooDeep,
+    /// Number of scripted functions over maximum limit.
+    TooManyFunctions,
     /// Literal exceeding the maximum size. Wrapped values are the data type name and the maximum size.
     LiteralTooLarge(String, usize),
     /// Break statement not inside a loop.
@@ -246,6 +248,7 @@ impl fmt::Display for ParseErrorType {
             Self::WrongDocComment => f.write_str("Doc-comment must be followed immediately by a function definition"),
             Self::WrongExport => f.write_str("Export statement can only appear at global level"),
             Self::ExprTooDeep => f.write_str("Expression exceeds maximum complexity"),
+            Self::TooManyFunctions => f.write_str("Number of functions defined exceeds maximum limit"),
             Self::LoopBreak => f.write_str("Break statement should only be used inside a loop"),
 
             #[allow(deprecated)]
diff --git a/src/types/scope.rs b/src/types/scope.rs
index 16bc229bb..e8622eaa8 100644
--- a/src/types/scope.rs
+++ b/src/types/scope.rs
@@ -1,7 +1,7 @@
 //! Module that defines the [`Scope`] type representing a function call-stack scope.
 
 use super::dynamic::{AccessMode, Variant};
-use crate::{Dynamic, Identifier, ImmutableString};
+use crate::{Dynamic, Identifier, ImmutableString, StaticVec};
 #[cfg(feature = "no_std")]
 use std::prelude::v1::*;
 use std::{
@@ -69,7 +69,7 @@ pub struct Scope<'a> {
     ///
     /// This `Vec` is not filled until needed because aliases are used rarely
     /// (only for `export` statements).
-    aliases: ThinVec<Box<[ImmutableString]>>,
+    aliases: ThinVec<StaticVec<ImmutableString>>,
     /// Phantom to keep the lifetime parameter in order not to break existing code.
     dummy: PhantomData<&'a ()>,
 }
@@ -819,10 +819,8 @@ impl Scope<'_> {
             self.aliases.resize(index + 1, <_>::default());
         }
         let aliases = self.aliases.get_mut(index).unwrap();
-        if aliases.is_empty() || !aliases.contains(&alias) {
-            let mut vec = std::mem::take(aliases).to_vec();
-            vec.push(alias);
-            *aliases = vec.into_boxed_slice();
+        if !aliases.contains(&alias) {
+            aliases.push(alias);
         }
         self
     }
diff --git a/tests/functions.rs b/tests/functions.rs
index 31f500574..8089abf93 100644
--- a/tests/functions.rs
+++ b/tests/functions.rs
@@ -1,5 +1,5 @@
 #![cfg(not(feature = "no_function"))]
-use rhai::{Dynamic, Engine, EvalAltResult, FnNamespace, Module, NativeCallContext, ParseErrorType, Shared, INT};
+use rhai::{Dynamic, Engine, EvalAltResult, FnNamespace, FuncRegistration, Module, NativeCallContext, ParseErrorType, Shared, INT};
 
 #[test]
 fn test_functions() {
@@ -84,8 +84,9 @@ fn test_functions_namespaces() {
     #[cfg(not(feature = "no_module"))]
     {
         let mut m = Module::new();
-        let hash = m.set_native_fn("test", || Ok(999 as INT));
-        m.update_fn_namespace(hash, FnNamespace::Global);
+
+        let f = || 999 as INT;
+        FuncRegistration::new("test").with_namespace(FnNamespace::Global).set_into_module(&mut m, f);
 
         engine.register_static_module("hello", m.into());
 
@@ -537,3 +538,39 @@ fn test_functions_is_def() {
         )
         .unwrap());
 }
+
+#[test]
+#[cfg(not(feature = "unchecked"))]
+fn test_functions_max() {
+    let mut engine = Engine::new();
+    engine.set_max_functions(5);
+
+    engine
+        .compile(
+            "
+            fn foo1() {}
+            fn foo2() {}
+            fn foo3() {}
+            fn foo4() {}
+            fn foo5() {}
+        ",
+        )
+        .unwrap();
+
+    assert!(matches!(
+        engine
+            .compile(
+                "
+                fn foo1() {}
+                fn foo2() {}
+                fn foo3() {}
+                fn foo4() {}
+                fn foo5() {}
+                fn foo6() {}
+            "
+            )
+            .expect_err("should err")
+            .err_type(),
+        ParseErrorType::TooManyFunctions
+    ))
+}
diff --git a/tests/modules.rs b/tests/modules.rs
index bf2dabfae..c06bf14c4 100644
--- a/tests/modules.rs
+++ b/tests/modules.rs
@@ -1,7 +1,7 @@
 #![cfg(not(feature = "no_module"))]
 use rhai::{
     module_resolvers::{DummyModuleResolver, StaticModuleResolver},
-    Dynamic, Engine, EvalAltResult, FnNamespace, ImmutableString, Module, ParseError, ParseErrorType, Scope, INT,
+    Dynamic, Engine, EvalAltResult, FnNamespace, FuncRegistration, ImmutableString, Module, ParseError, ParseErrorType, Scope, INT,
 };
 //
 #[cfg(all(not(feature = "no_function"), feature = "internals"))]
@@ -36,8 +36,9 @@ fn test_module_sub_module() {
     sub_module2.build_index();
     assert!(!sub_module2.contains_indexed_global_functions());
 
-    let super_hash = sub_module2.set_native_fn("super_inc", |x: &mut INT| Ok(*x + 1));
-    sub_module2.update_fn_namespace(super_hash, FnNamespace::Global);
+    let f = |x: &mut INT| *x + 1;
+    FuncRegistration::new("super_inc").with_namespace(FnNamespace::Global).set_into_module(&mut sub_module2, f);
+
     sub_module2.build_index();
     assert!(sub_module2.contains_indexed_global_functions());
 
@@ -90,11 +91,9 @@ fn test_module_resolver() {
 
     module.set_var("answer", 42 as INT);
     module.set_native_fn("sum", |x: INT, y: INT, z: INT, w: INT| Ok(x + y + z + w));
-    let double_hash = module.set_native_fn("double", |x: &mut INT| {
-        *x *= 2;
-        Ok(())
-    });
-    module.update_fn_namespace(double_hash, FnNamespace::Global);
+
+    let f = |x: &mut INT| *x *= 2;
+    FuncRegistration::new("double").with_namespace(FnNamespace::Global).set_into_module(&mut module, f);
 
     #[cfg(not(feature = "no_float"))]
     module.set_native_fn("sum_of_three_args", |target: &mut INT, a: INT, b: INT, c: rhai::FLOAT| {
diff --git a/tests/switch.rs b/tests/switch.rs
index e9be2bb62..94915713c 100644
--- a/tests/switch.rs
+++ b/tests/switch.rs
@@ -56,6 +56,7 @@ fn test_switch() {
             .unwrap(),
         3
     );
+    assert_eq!(engine.eval::<bool>("let x = 1..42; switch x { 1 => (), 2 => 'a', 1..42 => true }").unwrap(), true);
 
     assert_eq!(engine.eval_with_scope::<INT>(&mut scope, "switch 42 { 42 => 123, 42 => 999 }").unwrap(), 123);