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

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

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

Used to do a cheap reference-to-reference conversion.

This trait is similar to `AsMut` which is used for converting between mutable references. If you need to do a costly conversion it is better to implement `From` with type `&T` or write a custom function.

`AsRef` has the same signature as `Borrow`, but `Borrow` is different in few aspects:

- Unlike `AsRef`, `Borrow` has a blanket impl for any `T`, and can be used to accept either a reference or a value.
- `Borrow` also requires that `Hash`, `Eq` and `Ord` for borrowed value are equivalent to those of the owned value. For this reason, if you want to borrow only a single field of a struct you can implement `AsRef`, but not `Borrow`.

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

By using trait bounds we can accept arguments of different types as long as they can be converted to the specified type `T`.

For example: By creating a generic function that takes an `AsRef<str>` we express that we want to accept all references that can be converted to `&str` as an argument. Since both `String` and `&str` implement `AsRef<str>` we can accept both as input argument.

    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.

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## Implementors

### `impl AsRef<[u8]> for str`[src]

#### `fn as_ref(&self) -> &[u8]`[src]

### `impl AsRef<str> for str`[src]

#### `fn as_ref(&self) -> &str`[src]

### `impl<T> AsRef<[T]> for [T]`[src]

#### `fn as_ref(&self) -> &[T]`[src]

### `impl<T, '_> AsRef<[T]> for Iter<'_, T>`[src]

#### `fn as_ref(&self) -> &[T]`[src]

### `impl<T, const N: usize> AsRef<[T]> for [T; N]`[src]

#### `fn as_ref(&self) -> &[T]`[src]

### `impl<T: ?Sized, U: ?Sized, '_> AsRef<U> for &'_ T where
T: AsRef<U>,` [src]

#### `fn as_ref(&self) -> &U`[src]

### `impl<T: ?Sized, U: ?Sized, '_> AsRef<U> for &'_ mut T where
T: AsRef<U>,` [src]

#### `fn as_ref(&self) -> &U`[src]

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