AsMut in core::convert - Rust
Description: Used to do a cheap mutable-to-mutable reference conversion.
Keywords: rust, rustlang, rust-lang, AsMut

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

    pub trait AsMut<T: ?Sized> {
        fn as_mut(&mut self) -> &mut T;
    }

Expand description

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

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

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

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

# Examples

Using `AsMut` as trait bound for a generic function we can accept all mutable references that can be converted to type `&mut T`. Because `Box<T>` implements `AsMut<T>` we can write a function `add_one` that takes all arguments that can be converted to `&mut u64`. Because `Box<T>` implements `AsMut<T>`, `add_one` accepts arguments of type `&mut Box<u64>` as well:

    fn add_one<T: AsMut<u64>>(num: &mut T) {
        *num.as_mut() += 1;
    }

    let mut boxed_num = Box::new(0);
    add_one(&mut boxed_num);
    assert_eq!(*boxed_num, 1);

Run

## Required methods

[src]

#### fn as_mut(&mut self) -> &mut T

Performs the conversion.

## Implementors

1.51.0[src]

### impl AsMut<str> for str

[src]

### impl<T> AsMut<[T]> for [T]

[src]

### impl<T, const N: usize> AsMut<[T]> for [T; N]

[src]

### impl<T: ?Sized, U: ?Sized> AsMut<U> for &mut T where
T: AsMut<U>,