Trait alloc::borrow::Borrow1.0.0 [−] [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

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);

Implementors