std::ops::DerefMut - Rust
Description: API documentation for the Rust `DerefMut` trait in crate `std`.
Keywords: rust, rustlang, rust-lang, DerefMut

# 1.0.0[−][src]Trait std::ops::DerefMut

    #[lang = "deref_mut"]
    pub trait DerefMut: Deref {
        fn deref_mut(&mut self) -> &mut Self::Target;
    }

Used for mutable dereferencing operations, like in `*v = 1;`.

In addition to being used for explicit dereferencing operations with the (unary) `*` operator in mutable contexts, `DerefMut` is also used implicitly by the compiler in many circumstances. This mechanism is called '`Deref` coercion'. In immutable contexts, `Deref` is used.

Implementing `DerefMut` for smart pointers makes mutating the data behind them convenient, which is why they implement `DerefMut`. On the other hand, the rules regarding `Deref` and `DerefMut` were designed specifically to accommodate smart pointers. Because of this, `DerefMut` should only be implemented for smart pointers to avoid confusion.

For similar reasons, this trait should never fail. Failure during dereferencing can be extremely confusing when `DerefMut` is invoked implicitly.

# More on `Deref` coercion

If `T` implements `DerefMut<Target = U>`, and `x` is a value of type `T`, then:

- In mutable contexts, `*x` on non-pointer types is equivalent to `*DerefMut::deref_mut(&mut x)`.
- Values of type `&mut T` are coerced to values of type `&mut U`
- `T` implicitly implements all the (mutable) methods of the type `U`.

For more details, visit [the chapter in The Rust Programming Language] book as well as the reference sections on [the dereference operator] ref-deref-op, method resolution and type coercions.

# Examples

A struct with a single field which is modifiable by dereferencing the struct.

    use std::ops::{Deref, DerefMut};

    struct DerefMutExample<T> {
        value: T
    }

    impl<T> Deref for DerefMutExample<T> {
        type Target = T;

        fn deref(&self) -> &Self::Target {
            &self.value
        }
    }

    impl<T> DerefMut for DerefMutExample<T> {
        fn deref_mut(&mut self) -> &mut Self::Target {
            &mut self.value
        }
    }

    let mut x = DerefMutExample { value: 'a' };
    *x = 'b';
    assert_eq!('b', *x);Run

## Required methods

### `fn deref_mut(&mut self) -> &mut Self::Target`

Mutably dereferences the value.

Loading content...

## Implementors

### `impl DerefMut for String`[src]

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

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

####
ⓘImportant traits for &'_ mut I

### Important traits for &'_ mut I

`impl<'_, I> Iterator for &'_ mut I where
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<'_, F> Future for &'_ mut F where
F: Unpin + Future + ?Sized, type Output = <F as Future>::Output;impl<R: Read + ?Sized, '_> Read for &'_ mut Rimpl<W: Write + ?Sized, '_> Write for &'_ mut W`
`fn deref_mut(&mut self) -> &mut T`[src]

### `impl<'_, T> DerefMut for RefMut<'_, T> where
T: ?Sized,` [src]

####
ⓘImportant traits for &'_ mut I

### Important traits for &'_ mut I

`impl<'_, I> Iterator for &'_ mut I where
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<'_, F> Future for &'_ mut F where
F: Unpin + Future + ?Sized, type Output = <F as Future>::Output;impl<R: Read + ?Sized, '_> Read for &'_ mut Rimpl<W: Write + ?Sized, '_> Write for &'_ mut W`
`fn deref_mut(&mut self) -> &mut T`[src]

### `impl<'_, T> DerefMut for PeekMut<'_, T> where
T: Ord,` [src]

####
ⓘImportant traits for &'_ mut I

### Important traits for &'_ mut I

`impl<'_, I> Iterator for &'_ mut I where
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<'_, F> Future for &'_ mut F where
F: Unpin + Future + ?Sized, type Output = <F as Future>::Output;impl<R: Read + ?Sized, '_> Read for &'_ mut Rimpl<W: Write + ?Sized, '_> Write for &'_ mut W`
`fn deref_mut(&mut self) -> &mut T`[src]

### `impl<'a> DerefMut for IoSliceMut<'a>`[src]

####
ⓘImportant traits for &'_ [u8]

### Important traits for &'_ [u8]

`impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]`
`fn deref_mut(&mut self) -> &mut [u8]`[src]

### `impl<P> DerefMut for Pin<P> where
P: DerefMut,
<P as Deref>::Target: Unpin,` [src]

#### `fn deref_mut(&mut self) -> &mut <P as Deref>::Target`[src]

### `impl<T> DerefMut for Box<T> where
T: ?Sized,` [src]

####
ⓘImportant traits for &'_ mut I

### Important traits for &'_ mut I

`impl<'_, I> Iterator for &'_ mut I where
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<'_, F> Future for &'_ mut F where
F: Unpin + Future + ?Sized, type Output = <F as Future>::Output;impl<R: Read + ?Sized, '_> Read for &'_ mut Rimpl<W: Write + ?Sized, '_> Write for &'_ mut W`
`fn deref_mut(&mut self) -> &mut T`[src]

### `impl<T> DerefMut for ManuallyDrop<T> where
T: ?Sized,` [src]

####
ⓘImportant traits for &'_ mut I

### Important traits for &'_ mut I

`impl<'_, I> Iterator for &'_ mut I where
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<'_, F> Future for &'_ mut F where
F: Unpin + Future + ?Sized, type Output = <F as Future>::Output;impl<R: Read + ?Sized, '_> Read for &'_ mut Rimpl<W: Write + ?Sized, '_> Write for &'_ mut W`
`fn deref_mut(&mut self) -> &mut T`[src]

### `impl<T> DerefMut for AssertUnwindSafe<T>`[src]

####
ⓘImportant traits for &'_ mut I

### Important traits for &'_ mut I

`impl<'_, I> Iterator for &'_ mut I where
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<'_, F> Future for &'_ mut F where
F: Unpin + Future + ?Sized, type Output = <F as Future>::Output;impl<R: Read + ?Sized, '_> Read for &'_ mut Rimpl<W: Write + ?Sized, '_> Write for &'_ mut W`
`fn deref_mut(&mut self) -> &mut T`[src]

### `impl<T> DerefMut for Vec<T>`[src]

####
ⓘImportant traits for &'_ [u8]

### Important traits for &'_ [u8]

`impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]`
`fn deref_mut(&mut self) -> &mut [T]`[src]

### `impl<T: ?Sized, '_> DerefMut for MutexGuard<'_, T>`[src]

####
ⓘImportant traits for &'_ mut I

### Important traits for &'_ mut I

`impl<'_, I> Iterator for &'_ mut I where
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<'_, F> Future for &'_ mut F where
F: Unpin + Future + ?Sized, type Output = <F as Future>::Output;impl<R: Read + ?Sized, '_> Read for &'_ mut Rimpl<W: Write + ?Sized, '_> Write for &'_ mut W`
`fn deref_mut(&mut self) -> &mut T`[src]

### `impl<T: ?Sized, '_> DerefMut for RwLockWriteGuard<'_, T>`[src]

####
ⓘImportant traits for &'_ mut I

### Important traits for &'_ mut I

`impl<'_, I> Iterator for &'_ mut I where
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<'_, F> Future for &'_ mut F where
F: Unpin + Future + ?Sized, type Output = <F as Future>::Output;impl<R: Read + ?Sized, '_> Read for &'_ mut Rimpl<W: Write + ?Sized, '_> Write for &'_ mut W`
`fn deref_mut(&mut self) -> &mut T`[src]

Loading content...

# Help

## Keyboard Shortcuts

`?`
  Show this help dialog
`S`
  Focus the search field
`↑`
  Move up in search results
`↓`
  Move down in search results
`↹`
  Switch tab
`⏎`
  Go to active search result
`+`
  Expand all sections
`-`
  Collapse 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`)

Search multiple things at once by splitting your query with comma (e.g., `str,u8` or `String,struct:Vec,test`)