Trait sp_std::ops::DerefMut

#[lang = "deref_mut"]pub trait DerefMut: Deref {
    pub 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 (where T is neither a reference nor a raw pointer) 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 as well as the reference sections on the dereference operator, 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);

Required methods

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

Mutably dereferences the value.

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Implementations on Foreign Types

impl DerefMut for OsString

pub fn deref_mut(&mut self) -> &mut OsStr

impl<'a> DerefMut for IoSliceMut<'a>

pub fn deref_mut(&mut self) -> &mut [u8]

impl<T> DerefMut for AssertUnwindSafe<T>

pub fn deref_mut(&mut self) -> &mut T

impl<'a, 'f> DerefMut for VaList<'a, 'f> where
    'f: 'a, 

pub fn deref_mut(&mut self) -> &mut VaListImpl<'f>

impl<'_, T> DerefMut for &'_ mut T where
    T: ?Sized, 

pub fn deref_mut(&mut self) -> &mut T

impl<P> DerefMut for Pin<P> where
    P: DerefMut,
    <P as Deref>::Target: Unpin, 

pub fn deref_mut(&mut self) -> &mut <P as Deref>::Target

impl<'_, T> !DerefMut for &'_ T where
    T: ?Sized, 

impl<'_, T> DerefMut for PeekMut<'_, T> where
    T: Ord, 

pub fn deref_mut(&mut self) -> &mut T

impl DerefMut for String

pub fn deref_mut(&mut self) -> &mut str

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Implementors

impl<'_, T> DerefMut for RefMut<'_, T> where
    T: ?Sized, 

pub fn deref_mut(&mut self) -> &mut T

impl<'_, T> DerefMut for MutexGuard<'_, T> where
    T: ?Sized, 

pub fn deref_mut(&mut self) -> &mut T

impl<'_, T> DerefMut for RwLockWriteGuard<'_, T> where
    T: ?Sized, 

pub fn deref_mut(&mut self) -> &mut T

impl<T> DerefMut for ManuallyDrop<T> where
    T: ?Sized, 

pub fn deref_mut(&mut self) -> &mut T

impl<T, A> DerefMut for Box<T, A> where
    T: ?Sized,
    A: Allocator, 

pub fn deref_mut(&mut self) -> &mut T

impl<T, A> DerefMut for Vec<T, A> where
    A: Allocator, 

pub fn deref_mut(&mut self) -> &mut [T]

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