      1
      2
      3
      4
      5
      6
      7
      8
      9
     10
     11
     12
     13
     14
     15
     16
     17
     18
     19
     20
     21
     22
     23
     24
     25
     26
     27
     28
     29
     30
     31
     32
     33
     34
     35
     36
     37
     38
     39
     40
     41
     42
     43
     44
     45
     46
     47
     48
     49
     50
     51
     52
     53
     54
     55
     56
     57
     58
     59
     60
     61
     62
     63
     64
     65
     66
     67
     68
     69
     70
     71
     72
     73
     74
     75
     76
     77
     78
     79
     80
     81
     82
     83
     84
     85
     86
     87
     88
     89
     90
     91
     92
     93
     94
     95
     96
     97
     98
     99
    100
    101
    102
    103
    104
    105
    106
    107

    // Copyright 2014 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.

    //! A module for working with borrowed data.

    #![stable(feature = "rust1", since = "1.0.0")]

    /// A trait for borrowing data.
    ///
    /// In general, there may be several ways to "borrow" a piece of data.  The
    /// typical ways of borrowing a type `T` are `&T` (a shared borrow) and `&mut T`
    /// (a mutable borrow). But types like `Vec<T>` provide additional kinds of
    /// borrows: the borrowed slices `&[T]` and `&mut [T]`.
    ///
    /// When writing generic code, it is often desirable to abstract over all ways
    /// of borrowing data from a given type. That is the role of the `Borrow`
    /// trait: if `T: Borrow<U>`, then `&U` can be borrowed from `&T`.  A given
    /// type can be borrowed as multiple different types. In particular, `Vec<T>:
    /// Borrow<Vec<T>>` and `Vec<T>: Borrow<[T]>`.
    ///
    /// If you are implementing `Borrow` and both `Self` and `Borrowed` implement
    /// `Hash`, `Eq`, and/or `Ord`, they must produce the same result.
    ///
    /// `Borrow` is very similar to, but different than, `AsRef`. See
    /// [the book][book] for more.
    ///
    /// [book]: ../../book/first-edition/borrow-and-asref.html
    #[stable(feature = "rust1", since = "1.0.0")]
    pub trait Borrow<Borrowed: ?Sized> {
        /// Immutably borrows from an owned value.
        ///
        /// # Examples
        ///
        /// ```
        /// use std::borrow::Borrow;
        ///
        /// fn check<T: Borrow<str>>(s: T) {
        ///     assert_eq!("Hello", s.borrow());
        /// }
        ///
        /// let s = "Hello".to_string();
        ///
        /// check(s);
        ///
        /// let s = "Hello";
        ///
        /// check(s);
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        fn borrow(&self) -> &Borrowed;
    }

    /// A trait for mutably borrowing data.
    ///
    /// Similar to `Borrow`, but for mutable borrows.
    #[stable(feature = "rust1", since = "1.0.0")]
    pub trait BorrowMut<Borrowed: ?Sized> : Borrow<Borrowed> {
        /// Mutably borrows from an owned value.
        ///
        /// # Examples
        ///
        /// ```
        /// use std::borrow::BorrowMut;
        ///
        /// fn check<T: BorrowMut<[i32]>>(mut v: T) {
        ///     assert_eq!(&mut [1, 2, 3], v.borrow_mut());
        /// }
        ///
        /// let v = vec![1, 2, 3];
        ///
        /// check(v);
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        fn borrow_mut(&mut self) -> &mut Borrowed;
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<T: ?Sized> Borrow<T> for T {
        fn borrow(&self) -> &T { self }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<T: ?Sized> BorrowMut<T> for T {
        fn borrow_mut(&mut self) -> &mut T { self }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<'a, T: ?Sized> Borrow<T> for &'a T {
        fn borrow(&self) -> &T { &**self }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<'a, T: ?Sized> Borrow<T> for &'a mut T {
        fn borrow(&self) -> &T { &**self }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<'a, T: ?Sized> BorrowMut<T> for &'a mut T {
        fn borrow_mut(&mut self) -> &mut T { &mut **self }
    }

# Help

## Keyboard Shortcuts

?
  Show this help dialog
S
  Focus the search field
↑
  Move up in search results
↓
  Move down in search results
↹
  Switch tab
⏎
  Go to active search result
+ / -
  Collapse/expand all sections

## Search Tricks

Prefix searches with a type followed by a colon (e.g. `fn:`) to restrict the search to a given type.

Accepted types are: `fn`, `mod`, `struct`, `enum`, `trait`, `type`, `macro`, and `const`.

Search functions by type signature (e.g. `vec -> usize` or `* -> vec`)