Trait DerefMut 

pub trait DerefMut: Deref {
    // Required method
    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 “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

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 syn::token::And

impl DerefMut for rustmax::syn::token::And

impl DerefMut for syn::token::At

impl DerefMut for rustmax::syn::token::At

impl DerefMut for BStr

impl DerefMut for BString

impl DerefMut for BorrowedPayload<'_>

impl DerefMut for BoxBytes

impl DerefMut for ByteStr

impl DerefMut for ByteString

impl DerefMut for BytesMut

impl DerefMut for syn::token::Caret

impl DerefMut for rustmax::syn::token::Caret

impl DerefMut for rustls::client::client_conn::connection::ClientConnection

impl DerefMut for rustls::quic::connection::ClientConnection

impl DerefMut for syn::token::Colon

impl DerefMut for rustmax::syn::token::Colon

impl DerefMut for syn::token::Comma

impl DerefMut for rustmax::syn::token::Comma

impl DerefMut for rustls::conn::connection::Connection

impl DerefMut for rustls::quic::connection::Connection

impl DerefMut for DebouncedEvent

impl DerefMut for syn::token::Dollar

impl DerefMut for rustmax::syn::token::Dollar

impl DerefMut for syn::token::Dot

impl DerefMut for rustmax::syn::token::Dot

impl DerefMut for syn::token::Eq

impl DerefMut for rustmax::syn::token::Eq

impl DerefMut for Error

Available on crate feature std or non-anyhow_no_core_error only.

impl DerefMut for syn::token::Gt

impl DerefMut for rustmax::syn::token::Gt

impl DerefMut for syn::token::Lt

impl DerefMut for rustmax::syn::token::Lt

impl DerefMut for syn::token::Minus

impl DerefMut for rustmax::syn::token::Minus

impl DerefMut for syn::token::Not

impl DerefMut for rustmax::syn::token::Not

impl DerefMut for syn::token::Or

impl DerefMut for rustmax::syn::token::Or

impl DerefMut for OriginalUri

impl DerefMut for OsString

impl DerefMut for PathBuf

impl DerefMut for syn::token::Percent

impl DerefMut for rustmax::syn::token::Percent

impl DerefMut for syn::token::Plus

impl DerefMut for rustmax::syn::token::Plus

impl DerefMut for syn::token::Pound

impl DerefMut for rustmax::syn::token::Pound

impl DerefMut for syn::token::Question

impl DerefMut for rustmax::syn::token::Question

impl DerefMut for syn::token::Semi

impl DerefMut for rustmax::syn::token::Semi

impl DerefMut for rustls::server::server_conn::connection::ServerConnection

impl DerefMut for rustls::quic::connection::ServerConnection

impl DerefMut for syn::token::Slash

impl DerefMut for rustmax::syn::token::Slash

impl DerefMut for syn::token::Star

impl DerefMut for rustmax::syn::token::Star

impl DerefMut for String

impl DerefMut for syn::token::Tilde

impl DerefMut for rustmax::syn::token::Tilde

impl DerefMut for UnbufferedClientConnection

impl DerefMut for UnbufferedServerConnection

impl DerefMut for syn::token::Underscore

impl DerefMut for rustmax::syn::token::Underscore

impl<'a, B> DerefMut for MutBorrowedBit<'a, B>

where B: BitBlock,

impl<'a, R, T> DerefMut for lock_api::mutex::MappedMutexGuard<'a, R, T>

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

impl<'a, R, T> DerefMut for lock_api::rwlock::MappedRwLockWriteGuard<'a, R, T>

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

impl<'a, R, T> DerefMut for lock_api::mutex::MutexGuard<'a, R, T>

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

impl<'a, R, T> DerefMut for lock_api::rwlock::RwLockWriteGuard<'a, R, T>

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

impl<'a, T, A> DerefMut for rustmax::prelude::vec::PeekMut<'a, T, A>

where A: Allocator,

impl<'a, T, F> DerefMut for PoolGuard<'a, T, F>

where T: Send, F: Fn() -> T,

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

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

where T: ?Sized,

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

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

impl<'a> DerefMut for Shlex<'a>

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

impl<'s, T> DerefMut for SliceVec<'s, T>

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

where A: Alignment, T: ?Sized,

impl<A> DerefMut for tinyvec::arrayvec::ArrayVec<A>

where A: Array,

impl<A> DerefMut for SmallVec<A>

where A: Array,

impl<A> DerefMut for TinyVec<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 rustls::quic::connection::ConnectionCommon<Data>

impl<I> DerefMut for SubImage<I>

where I: DerefMut,

impl<K, V, S> DerefMut for AHashMap<K, V, S>

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: Deref, PinHelper<Ptr>: PinDerefMutHelper<Target = <Pin<Ptr> as Deref>::Target>,

impl<S> DerefMut for BlockingStream<S>

where S: Stream + Unpin,

impl<S> DerefMut for State<S>

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

where A: Alignment, T: ?Sized,

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

where A: Alignment,

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

where A: Allocator, T: ?Sized,

impl<T, A> DerefMut for GrayAlpha_v08<T, A>

impl<T, A> DerefMut for rustmax::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 Vec<T, A>

where A: Allocator,

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 once_cell::unsync::Lazy<T, F>

where F: FnOnce() -> T,

impl<T, F> DerefMut for once_cell::sync::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, N> DerefMut for GenericArray<T, N>

where N: ArrayLength<T>,

impl<T, S> DerefMut for AHashSet<T, S>

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

where U: ArraySize,

impl<T, U> DerefMut for rustmax::futures::lock::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, const CAP: usize> DerefMut for arrayvec::arrayvec::ArrayVec<T, CAP>

impl<T> !DerefMut for &T

where T: ?Sized,

impl<T> DerefMut for &mut T

where T: ?Sized,

impl<T> DerefMut for AssertUnwindSafe<T>

impl<T> DerefMut for AutoFinisher<T>

where T: AutoFinish,

impl<T> DerefMut for CachePadded<T>

impl<T> DerefMut for ConnectInfo<T>

impl<T> DerefMut for rustls::conn::ConnectionCommon<T>

impl<T> DerefMut for Extension<T>

impl<T> DerefMut for Flock<T>

where T: Flockable,

Available on crate feature fs and neither Redox OS nor Solaris only.

impl<T> DerefMut for Form<T>

impl<T> DerefMut for Json<T>

impl<T> DerefMut for ManuallyDrop<T>

where T: ?Sized,

impl<T> DerefMut for rustmax::std::sync::nonpoison::MappedMutexGuard<'_, T>

where T: ?Sized,

impl<T> DerefMut for rustmax::std::sync::MappedMutexGuard<'_, T>

where T: ?Sized,

impl<T> DerefMut for rustmax::std::sync::nonpoison::MappedRwLockWriteGuard<'_, T>

where T: ?Sized,

impl<T> DerefMut for rustmax::std::sync::MappedRwLockWriteGuard<'_, T>

where T: ?Sized,

impl<T> DerefMut for rustmax::std::sync::nonpoison::MutexGuard<'_, T>

where T: ?Sized,

impl<T> DerefMut for rustmax::std::sync::MutexGuard<'_, T>

where T: ?Sized,

impl<T> DerefMut for rustmax::futures::lock::MutexGuard<'_, T>

where T: ?Sized,

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

where T: ?Sized,

impl<T> DerefMut for Owned<T>

where T: Pointable + ?Sized,

impl<T> DerefMut for rustmax::futures::lock::OwnedMutexGuard<T>

where T: ?Sized,

impl<T> DerefMut for rustmax::tokio::sync::OwnedMutexGuard<T>

where T: ?Sized,

impl<T> DerefMut for OwnedRwLockWriteGuard<T>

where T: ?Sized,

impl<T> DerefMut for Path<T>

impl<T> DerefMut for PlaneData<T>

where T: Pixel,

impl<T> DerefMut for Query<T>

impl<T> DerefMut for ReadOnly<T>

where T: Immutable + ?Sized,

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

where T: ?Sized,

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

where T: ?Sized,

impl<T> DerefMut for rustmax::std::sync::nonpoison::RwLockWriteGuard<'_, T>

where T: ?Sized,

impl<T> DerefMut for rustmax::std::sync::RwLockWriteGuard<'_, T>

where T: ?Sized,

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

where T: ?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<T> DerefMut for UniquePtr<T>

where T: UniquePtrTarget + Unpin,

impl<Z> DerefMut for Zeroizing<Z>

where Z: Zeroize + ?Sized,

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