# Trait collections::borrow::Borrow 1.0.0 [−] [src]

    pub trait Borrow<Borrowed> where
        Borrowed: ?Sized, {
        fn borrow(&self) -> &Borrowed;
    }

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 for more.

## Required Methods

### `fn borrow(&self) -> &Borrowed`

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);Run

## Implementors

- `impl<T> Borrow<[T]> for [T; 17]`
- `impl<T> Borrow<[T]> for [T; 12]`
- `impl<T> Borrow<[T]> for [T; 0]`
- `impl<T> Borrow<[T]> for [T; 3]`
- `impl<T> Borrow<[T]> for [T; 24]`
- `impl<T> Borrow<[T]> for [T; 31]`
- `impl<T> Borrow<[T]> for [T; 21]`
- `impl<T> Borrow<[T]> for [T; 25]`
- `impl<T> Borrow<[T]> for [T; 20]`
- `impl<T> Borrow<[T]> for [T; 23]`
- `impl<T> Borrow<[T]> for [T; 15]`
- `impl<T> Borrow<[T]> for [T; 18]`
- `impl<T> Borrow<[T]> for [T; 30]`
- `impl<T> Borrow<[T]> for [T; 2]`
- `impl<'a, T> Borrow<T> for &'a T where
  T: ?Sized,`
- `impl<T> Borrow<[T]> for [T; 19]`
- `impl<T> Borrow<T> for T where
  T: ?Sized,`
- `impl<T> Borrow<[T]> for [T; 1]`
- `impl<T> Borrow<[T]> for [T; 11]`
- `impl<T> Borrow<[T]> for [T; 5]`
- `impl<T> Borrow<[T]> for [T; 16]`
- `impl<T> Borrow<[T]> for [T; 7]`
- `impl<T> Borrow<[T]> for [T; 6]`
- `impl<T> Borrow<[T]> for [T; 8]`
- `impl<T> Borrow<[T]> for [T; 22]`
- `impl<'a, T> Borrow<T> for &'a mut T where
  T: ?Sized,`
- `impl<T> Borrow<[T]> for [T; 10]`
- `impl<T> Borrow<[T]> for [T; 26]`
- `impl<T> Borrow<[T]> for [T; 27]`
- `impl<T> Borrow<[T]> for [T; 32]`
- `impl<T> Borrow<[T]> for [T; 28]`
- `impl<T> Borrow<[T]> for [T; 29]`
- `impl<T> Borrow<[T]> for [T; 4]`
- `impl<T> Borrow<[T]> for [T; 9]`
- `impl<T> Borrow<[T]> for [T; 13]`
- `impl<T> Borrow<[T]> for [T; 14]`
- `impl<T> Borrow<T> for Rc<T> where
  T: ?Sized,`
- `impl<T> Borrow<T> for Box<T> where
  T: ?Sized,`
- `impl<T> Borrow<T> for Arc<T> where
  T: ?Sized,`
- `impl<'a, B: ?Sized> Borrow<B> for Cow<'a, B> where
  B: ToOwned,
  <B as ToOwned>::Owned: 'a,`
- `impl<T> Borrow<[T]> for Vec<T>`
- `impl Borrow<str> for String`

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