Trait std::convert::AsMut

1.0.0· source [−]

pub trait AsMut<T> where
    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);