Trait DerefMut

1.0.0 (const: unstable) · Source

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

Expand description

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§

1.0.0 (const: unstable) · Source

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

Mutably dereferences the value.

Dyn Compatibility§

This trait is dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety".

Implementors§

§

impl DerefMut for BStr

§

impl DerefMut for BString

DerefMut

Trait DerefMut Copy item path

§Mutable deref coercion

§Fallibility

§Examples

Required Methods§

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

Dyn Compatibility§

Implementors§

impl DerefMut for BStr

impl DerefMut for BString

impl DerefMut for BorrowedPayload<'_>

impl DerefMut for Buffer<'_>

impl DerefMut for ByteStr

impl DerefMut for ByteString

impl DerefMut for BytesMut

impl DerefMut for ClientConnection

impl DerefMut for ClientConnection

impl DerefMut for ColoredString

impl DerefMut for Connection

impl DerefMut for Connection

impl DerefMut for Error

impl DerefMut for Function

impl DerefMut for InodeValFileWriteGuard

impl DerefMut for MmapMut

impl DerefMut for MmapMut

impl DerefMut for MutableBuffer

impl DerefMut for OsString

impl DerefMut for PathBuf

impl DerefMut for ServerConnection

impl DerefMut for ServerConnection

impl DerefMut for String

impl DerefMut for Termios

impl DerefMut for TrackedVec

impl DerefMut for TryString

impl DerefMut for UnbufferedClientConnection

impl DerefMut for UnbufferedServerConnection

impl DerefMut for VariableArgs

impl DerefMut for WasiInstanceGuardMut<'_>

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, A> DerefMut for alloc::vec::peek_mut::PeekMut<'a, T, A>where A: Allocator,

impl<'a, T, C> DerefMut for sharded_slab::pool::RefMut<'a, T, C>where T: Clear + Default, C: Config,

impl<'a, T, F> DerefMut for PoolGuard<'a, T, F>where T: Send, F: Fn() -> T,

impl<'a, T> DerefMut for AlignedCowVec<'a, T>where T: 'a, [T]: ToOwned, <[T] as ToOwned>::Owned: BorrowMut<[T]>,

impl<'a, T> DerefMut for Locked<'a, T>

impl<'a, T> DerefMut for Managed<'a, T>where T: 'a + ?Sized,

impl<'a, T> DerefMut for ManagedSlice<'a, T>where T: 'a,

impl<'a, T> DerefMut for MappedMutexGuard<'a, T>where T: ?Sized,

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

impl<'a> DerefMut for MaybeUninitSlice<'a>

impl<'i> DerefMut for DeArray<'i>

impl<A> DerefMut for SmallVec<A>where A: Array,

impl<B, T> DerefMut for Ref<B, T>where B: ByteSliceMut, T: FromBytes + IntoBytes + KnownLayout + Immutable + ?Sized,

impl<Data> DerefMut for ConnectionCommon<Data>

impl<K, V, T> DerefMut for MappedRefMut<'_, K, V, T>where K: Eq + Hash,

impl<K, V> DerefMut for RefMut<'_, K, V>where K: Eq + Hash,

impl<K, V> DerefMut for RefMutMulti<'_, K, V>where K: Eq + Hash,

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

impl<LenT, S> DerefMut for StringInner<LenT, S>where LenT: LenType, S: StringStorage + ?Sized,

impl<Ptr> DerefMut for Pin<Ptr>where Ptr: Deref, PinHelper<Ptr>: PinDerefMutHelper<Target = <Pin<Ptr> as Deref>::Target>,

impl<S> DerefMut for Ascii<S>

impl<S> DerefMut for BlockingStream<S>where S: Stream + Unpin,

impl<S> DerefMut for UniCase<S>

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

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

impl<T, A> DerefMut for alloc::collections::binary_heap::PeekMut<'_, T, A>where T: Ord, A: Allocator,

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

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

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

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

impl<T, C> DerefMut for OwnedRefMut<T, C>where T: Clear + Default, C: Config,

impl<T, E> DerefMut for Strategy<T, E>where T: ?Sized,

impl<T, F, S> DerefMut for ScopeGuard<T, F, S>where F: FnOnce(T), S: Strategy,

impl<T, F> DerefMut for DropGuard<T, F>where F: FnOnce(T),

impl<T, F> DerefMut for Lazy<T, F>where F: FnOnce() -> T,

impl<T, F> DerefMut for Lazy<T, F>where F: FnOnce() -> T,

impl<T, F> DerefMut for LazyCell<T, F>where F: FnOnce() -> T,

Trait DerefMut

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, A> DerefMut for alloc::vec::peek_mut::PeekMut<'a, T, A>
where A: Allocator,

impl<'a, T, C> DerefMut for sharded_slab::pool::RefMut<'a, T, C>
where T: Clear + Default, C: Config,

impl<'a, T, F> DerefMut for PoolGuard<'a, T, F>
where T: Send, F: Fn() -> T,

impl<'a, T> DerefMut for AlignedCowVec<'a, T>
where T: 'a, [T]: ToOwned, <[T] as ToOwned>::Owned: BorrowMut<[T]>,

impl<'a, T> DerefMut for Managed<'a, T>
where T: 'a + ?Sized,

impl<'a, T> DerefMut for ManagedSlice<'a, T>
where T: 'a,

impl<'a, T> DerefMut for MappedMutexGuard<'a, T>
where T: ?Sized,

impl<A> DerefMut for SmallVec<A>
where A: Array,

impl<B, T> DerefMut for Ref<B, T>
where B: ByteSliceMut, T: FromBytes + IntoBytes + KnownLayout + Immutable + ?Sized,

impl<K, V, T> DerefMut for MappedRefMut<'_, K, V, T>
where K: Eq + Hash,

impl<K, V> DerefMut for RefMut<'_, K, V>
where K: Eq + Hash,

impl<K, V> DerefMut for RefMutMulti<'_, K, V>
where K: Eq + Hash,

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

impl<LenT, S> DerefMut for StringInner<LenT, S>
where LenT: LenType, S: StringStorage + ?Sized,

impl<Ptr> DerefMut for Pin<Ptr>
where Ptr: Deref, PinHelper<Ptr>: PinDerefMutHelper<Target = <Pin<Ptr> as Deref>::Target>,

impl<S> DerefMut for BlockingStream<S>
where S: Stream + Unpin,

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

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

impl<T, A> DerefMut for alloc::collections::binary_heap::PeekMut<'_, T, A>
where T: Ord, A: Allocator,

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

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

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

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

impl<T, C> DerefMut for OwnedRefMut<T, C>
where T: Clear + Default, C: Config,

impl<T, E> DerefMut for Strategy<T, E>
where T: ?Sized,

impl<T, F, S> DerefMut for ScopeGuard<T, F, S>
where F: FnOnce(T), S: Strategy,

impl<T, F> DerefMut for DropGuard<T, F>
where F: FnOnce(T),

impl<T, F> DerefMut for Lazy<T, F>
where F: FnOnce() -> T,

impl<T, F> DerefMut for Lazy<T, F>
where F: FnOnce() -> T,

impl<T, F> DerefMut for LazyCell<T, F>
where F: FnOnce() -> T,

impl<T, F> DerefMut for LazyLock<T, F>
where F: FnOnce() -> T,

impl<T, F> DerefMut for Undo<T, F>
where F: FnOnce(T),

impl<T, Idx, K> DerefMut for FindMutView<'_, T, Idx, K>
where T: Ord, Idx: LenType, K: Kind,

impl<T, K, S> DerefMut for PeekMutInner<'_, T, K, S>
where T: Ord, K: Kind, S: VecStorage<T> + ?Sized,

impl<T, LenT, S> DerefMut for VecInner<T, LenT, S>
where LenT: LenType, S: VecStorage<T> + ?Sized,

impl<T, N> DerefMut for GenericArray<T, N>
where N: ArrayLength<T>,

impl<T, U> DerefMut for Array<T, U>
where U: ArraySize,

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

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> !DerefMut for &T
where T: ?Sized,

impl<T> DerefMut for &mut T
where T: ?Sized,

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

impl<T> DerefMut for Flock<T>
where T: Flockable,

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

impl<T> DerefMut for std::sync::nonpoison::mutex::MappedMutexGuard<'_, T>
where T: ?Sized,

impl<T> DerefMut for std::sync::poison::mutex::MappedMutexGuard<'_, T>
where T: ?Sized,

impl<T> DerefMut for std::sync::nonpoison::rwlock::MappedRwLockWriteGuard<'_, T>
where T: ?Sized,

impl<T> DerefMut for std::sync::poison::rwlock::MappedRwLockWriteGuard<'_, T>
where T: ?Sized,

impl<T> DerefMut for std::sync::nonpoison::mutex::MutexGuard<'_, T>
where T: ?Sized,

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

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

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

impl<T> DerefMut for Owned<T>
where T: Pointable + ?Sized,

impl<T> DerefMut for OwnedMutexGuard<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 ReadOnly<T>
where T: Immutable + ?Sized,

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

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

impl<T> DerefMut for std::sync::nonpoison::rwlock::RwLockWriteGuard<'_, T>
where T: ?Sized,

impl<T> DerefMut for std::sync::poison::rwlock::RwLockWriteGuard<'_, T>
where T: ?Sized,

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

impl<T> DerefMut for Seal<'_, T>
where T: NoUndef + Unpin + ?Sized,

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

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

impl<T> DerefMut for Unalign<T>
where T: Unaligned,

impl<W> DerefMut for DebugAbbrev<W>
where W: Writer,

impl<W> DerefMut for DebugAbbrev<W>
where W: Writer,

impl<W> DerefMut for DebugFrame<W>
where W: Writer,

impl<W> DerefMut for DebugFrame<W>
where W: Writer,

impl<W> DerefMut for DebugInfo<W>
where W: Writer,

impl<W> DerefMut for DebugInfo<W>
where W: Writer,

impl<W> DerefMut for DebugLine<W>
where W: Writer,

impl<W> DerefMut for DebugLine<W>
where W: Writer,