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]
43 lines
1.0 KiB
Rust
43 lines
1.0 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::ops::Deref;
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struct DerefWithHelper<H, T> {
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helper: H
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}
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trait Helper<T> {
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fn helper_borrow(&self) -> &T;
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}
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impl<T> Helper<T> for Option<T> {
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fn helper_borrow(&self) -> &T {
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self.as_ref().unwrap()
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}
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}
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impl<T, H: Helper<T>> Deref<T> for DerefWithHelper<H, T> {
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fn deref(&self) -> &T {
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self.helper.helper_borrow()
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}
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}
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struct Foo {x: int}
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impl Foo {
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fn foo(&self) -> int {self.x}
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}
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pub fn main() {
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let x: DerefWithHelper<Option<Foo>, Foo> = DerefWithHelper { helper: Some(Foo {x: 5}) };
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assert!(x.foo() == 5);
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}
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