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]
44 lines
1.1 KiB
Rust
44 lines
1.1 KiB
Rust
// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
|
|
// file at the top-level directory of this distribution and at
|
|
// http://rust-lang.org/COPYRIGHT.
|
|
//
|
|
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
|
|
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
|
|
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
|
|
// option. This file may not be copied, modified, or distributed
|
|
// except according to those terms.
|
|
|
|
enum ast<'a> {
|
|
num(uint),
|
|
add(&'a ast<'a>, &'a ast<'a>)
|
|
}
|
|
|
|
fn build() {
|
|
let x = num(3u);
|
|
let y = num(4u);
|
|
let z = add(&x, &y);
|
|
compute(&z);
|
|
}
|
|
|
|
fn compute(x: &ast) -> uint {
|
|
match *x {
|
|
num(x) => { x }
|
|
add(x, y) => { compute(x) + compute(y) }
|
|
}
|
|
}
|
|
|
|
fn map_nums<'a,'b>(x: &ast, f: |uint| -> uint) -> &'a ast<'b> {
|
|
match *x {
|
|
num(x) => {
|
|
return &num(f(x)); //~ ERROR borrowed value does not live long enough
|
|
}
|
|
add(x, y) => {
|
|
let m_x = map_nums(x, |z| f(z));
|
|
let m_y = map_nums(y, |z| f(z));
|
|
return &add(m_x, m_y); //~ ERROR borrowed value does not live long enough
|
|
}
|
|
}
|
|
}
|
|
|
|
fn main() {}
|