Trait std::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.


use std::borrow::Borrow;

fn check<T: Borrow<str>>(s: T) {
    assert_eq!("Hello", s.borrow());

let s = "Hello".to_string();


let s = "Hello";