Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Document const_constructor feature #677

Merged
merged 1 commit into from
Oct 27, 2019
Merged

Document const_constructor feature #677

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
19 changes: 12 additions & 7 deletions src/items/functions.md
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -180,12 +180,13 @@ aborts the process by executing an illegal instruction.

## Const functions

Functions qualified with the `const` keyword are const functions. _Const
functions_ can be called from within [const context]s. When called from a const
context, the function is interpreted by the compiler at compile time. The
interpretation happens in the environment of the compilation target and not the
host. So `usize` is `32` bits if you are compiling against a `32` bit system,
irrelevant of whether you are building on a `64` bit or a `32` bit system.
Functions qualified with the `const` keyword are const functions, as are
[tuple struct] and [tuple variant] constructors. _Const functions_ can be
called from within [const context]s. When called from a const context, the
function is interpreted by the compiler at compile time. The interpretation
happens in the environment of the compilation target and not the host. So
`usize` is `32` bits if you are compiling against a `32` bit system, irrelevant
of whether you are building on a `64` bit or a `32` bit system.

If a const function is called outside a [const context], it is indistinguishable
from any other function. You can freely do anything with a const function that
Expand Down Expand Up @@ -214,7 +215,9 @@ Exhaustive list of permitted structures in const functions:
are all permitted.

This rule also applies to type parameters of impl blocks that
contain const methods
contain const methods.

This does not apply to tuple struct and tuple variant constructors.

* Arithmetic and comparison operators on integers
* All boolean operators except for `&&` and `||` which are banned since
Expand Down Expand Up @@ -360,6 +363,8 @@ attributes macros.
[_Type_]: ../types.md#type-expressions
[_WhereClause_]: generics.md#where-clauses
[const context]: ../const_eval.md#const-context
[tuple struct]: structs.md
[tuple variant]: enumerations.md
[external block]: external-blocks.md
[path]: ../paths.md
[block]: ../expressions/block-expr.md
Expand Down