110 lines
3.3 KiB
Rust
110 lines
3.3 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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//! A module for working with borrowed data.
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#![stable(feature = "rust1", since = "1.0.0")]
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use marker::Sized;
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/// A trait for borrowing data.
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///
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/// In general, there may be several ways to "borrow" a piece of data. The
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/// typical ways of borrowing a type `T` are `&T` (a shared borrow) and `&mut T`
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/// (a mutable borrow). But types like `Vec<T>` provide additional kinds of
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/// borrows: the borrowed slices `&[T]` and `&mut [T]`.
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///
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/// When writing generic code, it is often desirable to abstract over all ways
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/// of borrowing data from a given type. That is the role of the `Borrow`
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/// trait: if `T: Borrow<U>`, then `&U` can be borrowed from `&T`. A given
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/// type can be borrowed as multiple different types. In particular, `Vec<T>:
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/// Borrow<Vec<T>>` and `Vec<T>: Borrow<[T]>`.
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///
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/// If you are implementing `Borrow` and both `Self` and `Borrowed` implement
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/// `Hash`, `Eq`, and/or `Ord`, they must produce the same result.
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///
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/// `Borrow` is very similar to, but different than, `AsRef`. See
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/// [the book][book] for more.
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///
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/// [book]: ../../book/borrow-and-asref.html
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#[stable(feature = "rust1", since = "1.0.0")]
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pub trait Borrow<Borrowed: ?Sized> {
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/// Immutably borrows from an owned value.
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///
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/// # Examples
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///
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/// ```
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/// use std::borrow::Borrow;
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///
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/// fn check<T: Borrow<str>>(s: T) {
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/// assert_eq!("Hello", s.borrow());
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/// }
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///
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/// let s = "Hello".to_string();
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///
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/// check(s);
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///
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/// let s = "Hello";
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///
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/// check(s);
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/// ```
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#[stable(feature = "rust1", since = "1.0.0")]
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fn borrow(&self) -> &Borrowed;
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}
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/// A trait for mutably borrowing data.
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///
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/// Similar to `Borrow`, but for mutable borrows.
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#[stable(feature = "rust1", since = "1.0.0")]
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pub trait BorrowMut<Borrowed: ?Sized> : Borrow<Borrowed> {
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/// Mutably borrows from an owned value.
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///
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/// # Examples
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///
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/// ```
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/// use std::borrow::BorrowMut;
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///
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/// fn check<T: BorrowMut<[i32]>>(mut v: T) {
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/// assert_eq!(&mut [1, 2, 3], v.borrow_mut());
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/// }
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///
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/// let v = vec![1, 2, 3];
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///
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/// check(v);
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/// ```
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#[stable(feature = "rust1", since = "1.0.0")]
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fn borrow_mut(&mut self) -> &mut Borrowed;
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<T: ?Sized> Borrow<T> for T {
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fn borrow(&self) -> &T { self }
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<T: ?Sized> BorrowMut<T> for T {
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fn borrow_mut(&mut self) -> &mut T { self }
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<'a, T: ?Sized> Borrow<T> for &'a T {
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fn borrow(&self) -> &T { &**self }
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<'a, T: ?Sized> Borrow<T> for &'a mut T {
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fn borrow(&self) -> &T { &**self }
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<'a, T: ?Sized> BorrowMut<T> for &'a mut T {
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fn borrow_mut(&mut self) -> &mut T { &mut **self }
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}
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