rust-lang/rust — pull request #15767 by pcwalton (2014-07-18 04:54:02+00:00)
Title: librustc: Implement lifetime elision.

This implements RFC 39. Omitted lifetimes in return values will now be
inferred to more useful defaults, and an error is reported if a lifetime
in a return type is omitted and one of the two lifetime elision rules
does not specify what it should be.

This primarily breaks two uncommon code patterns. The first is this:

unsafe fn get_foo_out_of_thin_air() -> &Foo {
...
}

This should be changed to:

unsafe fn get_foo_out_of_thin_air() -> &'static Foo {
...
}

The second pattern that needs to be changed is this:

enum MaybeBorrowed<'a> {
Borrowed(&'a str),
Owned(String),
}

fn foo() -> MaybeBorrowed {
Owned(format!("hello world"))
}

Change code like this to:

enum MaybeBorrowed<'a> {
Borrowed(&'a str),
Owned(String),
}

fn foo() -> MaybeBorrowed<'static> {
Owned(format!("hello world"))
}

Closes #15552.

[breaking-change]

r? @nick29581