core::convert::AsRef - Rust
Description: API documentation for the Rust `AsRef` trait in crate `core`.
Keywords: rust, rustlang, rust-lang, AsRef

# Trait core::convert::AsRef 1.0.0 [−] [src]

    pub trait AsRef<T: ?Sized> {
        fn as_ref(&self) -> &T;
    }

A cheap reference-to-reference conversion. Used to convert a value to a reference value within generic code.

`AsRef` is very similar to, but serves a slightly different purpose than, `Borrow`.

`AsRef` is to be used when wishing to convert to a reference of another type. `Borrow` is more related to the notion of taking the reference. It is useful when wishing to abstract over the type of reference (`&T`, `&mut T`) or allow both the referenced and owned type to be treated in the same manner.

The key difference between the two traits is the intention:

- Use `AsRef` when goal is to simply convert into a reference
- Use `Borrow` when goal is related to writing code that is agnostic to the type of borrow and if is reference or value

See the book for a more detailed comparison.

Note: this trait must not fail. If the conversion can fail, use a dedicated method which returns an `Option<T>` or a `Result<T, E>`.

# Generic Implementations

- `AsRef` auto-dereferences if the inner type is a reference or a mutable reference (e.g.: `foo.as_ref()` will work the same if `foo` has type `&mut Foo` or `&&mut Foo`)

# Examples

Both `String` and `&str` implement `AsRef<str>`:

    fn is_hello<T: AsRef<str>>(s: T) {
       assert_eq!("hello", s.as_ref());
    }

    let s = "hello";
    is_hello(s);

    let s = "hello".to_string();
    is_hello(s);Run

## Required Methods

### `fn as_ref(&self) -> &T`

Performs the conversion.

## Implementors

- `impl<'a, T: ?Sized, U: ?Sized> AsRef<U> for &'a T where
  T: AsRef<U>,`
- `impl<'a, T: ?Sized, U: ?Sized> AsRef<U> for &'a mut T where
  T: AsRef<U>,`
- `impl<T> AsRef<[T]> for [T]`
- `impl AsRef<str> for str`
- `impl<T> AsRef<[T]> for [T; 0]`
- `impl<T> AsRef<[T]> for [T; 1]`
- `impl<T> AsRef<[T]> for [T; 2]`
- `impl<T> AsRef<[T]> for [T; 3]`
- `impl<T> AsRef<[T]> for [T; 4]`
- `impl<T> AsRef<[T]> for [T; 5]`
- `impl<T> AsRef<[T]> for [T; 6]`
- `impl<T> AsRef<[T]> for [T; 7]`
- `impl<T> AsRef<[T]> for [T; 8]`
- `impl<T> AsRef<[T]> for [T; 9]`
- `impl<T> AsRef<[T]> for [T; 10]`
- `impl<T> AsRef<[T]> for [T; 11]`
- `impl<T> AsRef<[T]> for [T; 12]`
- `impl<T> AsRef<[T]> for [T; 13]`
- `impl<T> AsRef<[T]> for [T; 14]`
- `impl<T> AsRef<[T]> for [T; 15]`
- `impl<T> AsRef<[T]> for [T; 16]`
- `impl<T> AsRef<[T]> for [T; 17]`
- `impl<T> AsRef<[T]> for [T; 18]`
- `impl<T> AsRef<[T]> for [T; 19]`
- `impl<T> AsRef<[T]> for [T; 20]`
- `impl<T> AsRef<[T]> for [T; 21]`
- `impl<T> AsRef<[T]> for [T; 22]`
- `impl<T> AsRef<[T]> for [T; 23]`
- `impl<T> AsRef<[T]> for [T; 24]`
- `impl<T> AsRef<[T]> for [T; 25]`
- `impl<T> AsRef<[T]> for [T; 26]`
- `impl<T> AsRef<[T]> for [T; 27]`
- `impl<T> AsRef<[T]> for [T; 28]`
- `impl<T> AsRef<[T]> for [T; 29]`
- `impl<T> AsRef<[T]> for [T; 30]`
- `impl<T> AsRef<[T]> for [T; 31]`
- `impl<T> AsRef<[T]> for [T; 32]`
- `impl<'a, T> AsRef<[T]> for Iter<'a, T>`
- `impl AsRef<[u8]> for str`

# Help

## Keyboard Shortcuts

?
  Show this help dialog
S
  Focus the search field
⇤
  Move up in search results
⇥
  Move down in search results
⏎
  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`)