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]
82 lines
1.7 KiB
Rust
82 lines
1.7 KiB
Rust
// Copyright 2014 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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use std::cell::Cell;
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use std::ops::{Deref, DerefMut};
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#[deriving(PartialEq)]
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struct DerefCounter<T> {
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count_imm: Cell<uint>,
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count_mut: uint,
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value: T
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}
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impl<T> DerefCounter<T> {
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fn new(value: T) -> DerefCounter<T> {
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DerefCounter {
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count_imm: Cell::new(0),
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count_mut: 0,
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value: value
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}
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}
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fn counts(&self) -> (uint, uint) {
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(self.count_imm.get(), self.count_mut)
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}
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}
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impl<T> Deref<T> for DerefCounter<T> {
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fn deref(&self) -> &T {
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self.count_imm.set(self.count_imm.get() + 1);
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&self.value
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}
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}
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impl<T> DerefMut<T> for DerefCounter<T> {
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fn deref_mut(&mut self) -> &mut T {
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self.count_mut += 1;
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&mut self.value
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}
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}
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#[deriving(PartialEq, Show)]
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struct Point {
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x: int,
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y: int
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}
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impl Point {
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fn get(&self) -> (int, int) {
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(self.x, self.y)
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}
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}
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pub fn main() {
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let mut p = DerefCounter::new(Point {x: 0, y: 0});
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let _ = p.x;
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assert_eq!(p.counts(), (1, 0));
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let _ = &p.x;
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assert_eq!(p.counts(), (2, 0));
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let _ = &mut p.y;
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assert_eq!(p.counts(), (2, 1));
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p.x += 3;
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assert_eq!(p.counts(), (2, 2));
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p.get();
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assert_eq!(p.counts(), (2, 3));
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// Check the final state.
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assert_eq!(*p, Point {x: 3, y: 0});
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}
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