From 5e8d2736db2a2fbb3e2f4a408c462d9c43111b51 Mon Sep 17 00:00:00 2001
From: Niko Matsakis <niko@alum.mit.edu>
Date: Tue, 16 Sep 2014 14:26:03 -0400
Subject: [PATCH] Permit multiple lifetime bounds on parameter types.
---
...0049-bounds-on-object-and-generic-types.md | 24 +++----------------
1 file changed, 3 insertions(+), 21 deletions(-)
diff --git a/active/0049-bounds-on-object-and-generic-types.md b/active/0049-bounds-on-object-and-generic-types.md
index 5fc8dd1508f..558cacea78f 100644
--- a/active/0049-bounds-on-object-and-generic-types.md
+++ b/active/0049-bounds-on-object-and-generic-types.md
@@ -69,24 +69,6 @@ declared:
Here, the constraint `T:'a` indicates that the data being iterated
over must live at least as long as the collection (logically enough).
-### At most one explicit lifetime bound is permitted
-
-For simplicity, we permit at most one *explicit* lifetime bound on any
-given parameter type. That means that the following function is illegal:
-
- fn foo<'a,'b,A:'a+'b>() { ... }
-
-Remember that if there are multiple lifetime bounds, it implies that
-all of them must hold. That means that if, in fact, `A` outlives both
-`'a` and `'b` then either one of them is shorter than the other, the
-two are the same, or there is a third lifetime that outlives them
-both. Therefore, the function above can be rewritten as follows (using
-explicit lifetime bounds, specified below):
-
- fn foo<'a,'b,'c:'a+'b,A:'c>() { ... }
-
-As far as I know, this situation has not arisen once in the codebase.
-
## Lifetime bounds on object types
Like parameters, all object types have a lifetime bound. Unlike
@@ -113,9 +95,9 @@ Here are some examples:
// IsStatic+'a 'static+'a
// IsStatic+Is<'a>+'b 'static,'a,'b
-In general no object type is permitted to have zero bounds. Therefore,
-if an object type with no derivable bounds appears, we will supply a
-default lifetime using the normal rules:
+Object types must have exactly one bound -- zero bounds is not
+acceptable. Therefore, if an object type with no derivable bounds
+appears, we will supply a default lifetime using the normal rules:
trait Writer { /* no derivable bounds */ }
struct Foo<'a> {