6f99a27886
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]
46 lines
1.4 KiB
Rust
46 lines
1.4 KiB
Rust
// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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fn of<'a,T>() -> |T|:'a { fail!(); }
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fn subtype<T>(x: |T|) { fail!(); }
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fn test_fn<'x,'y,'z,T>(_x: &'x T, _y: &'y T, _z: &'z T) {
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// Here, x, y, and z are free. Other letters
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// are bound. Note that the arrangement
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// subtype::<T1>(of::<T2>()) will typecheck
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// iff T1 <: T2.
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subtype::< <'a>|&'a T|>(
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of::< <'a>|&'a T|>());
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subtype::< <'a>|&'a T|>(
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of::< <'b>|&'b T|>());
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subtype::< <'b>|&'b T|>(
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of::<|&'x T|>());
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subtype::<|&'x T|>(
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of::< <'b>|&'b T|>()); //~ ERROR mismatched types
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subtype::< <'a,'b>|&'a T, &'b T|>(
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of::< <'a>|&'a T, &'a T|>());
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subtype::< <'a>|&'a T, &'a T|>(
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of::< <'a,'b>|&'a T, &'b T|>()); //~ ERROR mismatched types
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subtype::< <'a,'b>|&'a T, &'b T|>(
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of::<|&'x T, &'y T|>());
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subtype::<|&'x T, &'y T|>(
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of::< <'a,'b>|&'a T, &'b T|>()); //~ ERROR mismatched types
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}
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fn main() {}
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