Trait DerefMut

pub trait DerefMut: Deref {
    // Required method
    const fn deref_mut(&mut self) -> &mut Self::Target;
}

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

Re-exported from core::ops:: .

---

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 “mutable deref coercion”. In immutable contexts, Deref is used.

Warning: Deref coercion is a powerful language feature which has far-reaching implications for every type that implements DerefMut. The compiler will silently insert calls to DerefMut::deref_mut. For this reason, one should be careful about implementing DerefMut and only do so when mutable deref coercion is desirable. See the Deref docs for advice on when this is typically desirable or undesirable.

Types that implement DerefMut or Deref are often called “smart pointers” and the mechanism of deref coercion has been specifically designed to facilitate the pointer-like behavior that name suggests. Often, the purpose of a “smart pointer” type is to change the ownership semantics of a contained value (for example, Rc or Cow) or the storage semantics of a contained value (for example, Box).

Mutable deref coercion

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

• In mutable contexts, *v (where T is neither a reference nor a raw pointer) is equivalent to *DerefMut::deref_mut(&mut v).
• 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.

Fallibility

This trait’s method should never unexpectedly fail. Deref coercion means the compiler will often insert calls to DerefMut::deref_mut implicitly. Failure during dereferencing can be extremely confusing when DerefMut is invoked implicitly. In the majority of uses it should be infallible, though it may be acceptable to panic if the type is misused through programmer error, for example.

However, infallibility is not enforced and therefore not guaranteed. As such, unsafe code should not rely on infallibility in general for soundness.

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.value);

Required Methods

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

Mutably dereferences the value.

Implementors

impl DerefMut for ByteStr

impl DerefMut for ByteString

impl DerefMut for BoxBytes

impl DerefMut for Column

impl DerefMut for HGrid

impl DerefMut for Row

impl DerefMut for VGrid

impl DerefMut for AndroidWindow

impl DerefMut for FPoint

impl DerefMut for FRect

impl DerefMut for devela::_dep::sdl2::rect::Point

impl DerefMut for devela::_dep::sdl2::rect::Rect

impl DerefMut for devela::_dep::sdl3::rect::Point

impl DerefMut for devela::_dep::sdl3::rect::Rect

impl DerefMut for devela::_dep::sdl3::surface::Surface<'_>

impl DerefMut for devela::_dep::sdl3::video::WindowSurfaceRef<'_>

impl DerefMut for Components

impl DerefMut for Disks

impl DerefMut for Groups

impl DerefMut for Users

impl DerefMut for DocumentMut

impl DerefMut for Affine2

impl DerefMut for Affine3A

impl DerefMut for Mat2

impl DerefMut for Quat

impl DerefMut for Vec3A

impl DerefMut for Vec4

impl DerefMut for DAffine2

impl DerefMut for DAffine3

impl DerefMut for OsString

impl DerefMut for PathBuf

impl DerefMut for devela::all::String

impl DerefMut for BytesMut

impl<'a> DerefMut for devela::_dep::sdl2::surface::Surface<'a>

impl<'a> DerefMut for devela::_dep::sdl2::video::WindowSurfaceRef<'a>

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

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

where 'f: 'a,

impl<'a, CB> DerefMut for AudioDeviceLockGuard<'a, CB>

where CB: AudioCallback,

impl<'a, R, T> DerefMut for MappedMutexGuard<'a, R, T>

where R: RawMutex + 'a, T: 'a + ?Sized,

impl<'a, R, T> DerefMut for MappedRwLockWriteGuard<'a, R, T>

where R: RawRwLock + 'a, T: 'a + ?Sized,

impl<'a, R, T> DerefMut for MutexGuard<'a, R, T>

where R: RawMutex + 'a, T: 'a + ?Sized,

impl<'a, R, T> DerefMut for RwLockWriteGuard<'a, R, T>

where R: RawRwLock + 'a, T: 'a + ?Sized,

impl<'a, T> DerefMut for devela::_dep::bumpalo::boxed::Box<'a, T>

where T: ?Sized,

impl<'a, T> DerefMut for devela::_dep::tokio::sync::MappedMutexGuard<'a, T>

where T: ?Sized,

impl<'bump> DerefMut for devela::_dep::bumpalo::collections::String<'bump>

impl<'bump, T> DerefMut for devela::_dep::bumpalo::collections::Vec<'bump, T>

where T: 'bump,

impl<A> DerefMut for SmallVec<A>

where A: Array,

impl<DST: ?Sized, BUF: DstBuf> DerefMut for DstQueuePopHandle<'_, DST, BUF>

Available on crate feature unsafe_layout only.

impl<DST: ?Sized, BUF: DstBuf> DerefMut for DstValue<DST, BUF>

Available on crate feature unsafe_layout only.

impl<I> DerefMut for SubImage<I>

where I: DerefMut,

impl<L, R> DerefMut for Either<L, R>

where L: DerefMut, R: DerefMut<Target = <L as Deref>::Target>,

impl<P, Container> DerefMut for ImageBuffer<P, Container>

where P: Pixel, Container: Deref<Target = [<P as Pixel>::Subpixel]> + DerefMut,

impl<Ptr> DerefMut for Pin<Ptr>

where Ptr: DerefMut, <Ptr as Deref>::Target: Unpin,

impl<T> !DerefMut for &T

where T: ?Sized,

impl<T> DerefMut for &mut T

where T: ?Sized,

impl<T> DerefMut for ThinBox<T>

where T: ?Sized,

impl<T> DerefMut for devela::_dep::_std::sync::MappedMutexGuard<'_, T>

where T: ?Sized,

impl<T> DerefMut for devela::_dep::_std::sync::MappedRwLockWriteGuard<'_, T>

where T: ?Sized,

impl<T> DerefMut for PyRefMut<'_, T>

where T: PyClass<Frozen = False>,

impl<T> DerefMut for devela::_dep::tokio::sync::MutexGuard<'_, T>

where T: ?Sized,

impl<T> DerefMut for OwnedMutexGuard<T>

where T: ?Sized,

impl<T> DerefMut for OwnedRwLockWriteGuard<T>

where T: ?Sized,

impl<T> DerefMut for RwLockMappedWriteGuard<'_, T>

where T: ?Sized,

impl<T> DerefMut for devela::_dep::tokio::sync::RwLockWriteGuard<'_, T>

where T: ?Sized,

impl<T> DerefMut for Clamped<T>

impl<T> DerefMut for BareBox<T>

impl<T> DerefMut for CacheAlign<T>

impl<T> DerefMut for ManuallyDrop<T>

where T: ?Sized,

impl<T> DerefMut for devela::all::MutexGuard<'_, T>

where T: ?Sized,

impl<T> DerefMut for AssertUnwindSafe<T>

impl<T> DerefMut for RefMut<'_, T>

where T: ?Sized,

impl<T> DerefMut for devela::all::RwLockWriteGuard<'_, T>

where T: ?Sized,

impl<T> DerefMut for CachePadded<T>

impl<T> DerefMut for InputPublishGuard<'_, T>

where T: Send,

impl<T> DerefMut for Owned<T>

where T: Pointable + ?Sized,

impl<T> DerefMut for ShardedLockWriteGuard<'_, T>

where T: ?Sized,

impl<T, A> DerefMut for PeekMut<'_, T, A>

where T: Ord, A: Allocator,

impl<T, A> DerefMut for UniqueRc<T, A>

where A: Allocator, T: ?Sized,

impl<T, A> DerefMut for devela::all::Box<T, A>

where A: Allocator, T: ?Sized,

impl<T, A> DerefMut for devela::all::Vec<T, A>

where A: Allocator,

impl<T, F> DerefMut for devela::_dep::fltk::utils::oncelock::Lazy<T, F>

where F: FnOnce() -> T,

impl<T, F> DerefMut for Lazy<T, F>

where F: FnOnce() -> T,

impl<T, F, S> DerefMut for scopeguard::ScopeGuard<T, F, S>

where F: FnOnce(T), S: Strategy,

impl<T, F: FnOnce(T, &S), S> DerefMut for devela::code::ScopeGuard<T, F, S>

impl<T, U> DerefMut for OwnedMappedMutexGuard<T, U>

where T: ?Sized, U: ?Sized,

impl<T, U> DerefMut for OwnedRwLockMappedWriteGuard<T, U>

where T: ?Sized, U: ?Sized,

impl<T, const CAP: usize> DerefMut for arrayvec::arrayvec::ArrayVec<T, CAP>

impl<T, const CAP: usize> DerefMut for DstArray<T, CAP>

Available on crate feature unsafe_layout only.

impl<T, const CAP: usize, S: Storage> DerefMut for Array<T, CAP, S>

impl<T, const N: usize> DerefMut for devela::_dep::ureq::unversioned::resolver::ArrayVec<T, N>

impl<T: Any> DerefMut for Current<T>

Available on crate features std and unsafe_layout only.

impl<Z> DerefMut for Zeroizing<Z>

where Z: Zeroize,

impl<const CAP: usize> DerefMut for ArrayString<CAP>