pub trait DerefMut: Deref {
// Required method
fn deref_mut(&mut self) -> &mut Self::Target;
}std only.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(whereTis neither a reference nor a raw pointer) is equivalent to*DerefMut::deref_mut(&mut v). - Values of type
&mut Tare coerced to values of type&mut U Timplicitly implements all the (mutable) methods of the typeU.
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§
Implementors§
impl DerefMut for PathBuf
impl DerefMut for devela::all::String
impl DerefMut for OsString
impl DerefMut for BoxBytes
impl DerefMut for Buffer<'_>
impl DerefMut for Components
impl DerefMut for Disks
impl DerefMut for Groups
impl DerefMut for Users
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 BytesMut
impl<'a> DerefMut for IoSliceMut<'a>
impl<'a, 'f> DerefMut for VaList<'a, 'f>where
'f: 'a,
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<'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>
unsafe_layout only.impl<DST: ?Sized, BUF: DstBuf> DerefMut for DstValue<DST, BUF>
unsafe_layout only.impl<L, R> DerefMut for Either<L, R>
impl<Ptr> DerefMut for Pin<Ptr>
impl<T> !DerefMut for &Twhere
T: ?Sized,
impl<T> DerefMut for &mut Twhere
T: ?Sized,
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 AssertUnwindSafe<T>
impl<T> DerefMut for RefMut<'_, T>where
T: ?Sized,
impl<T> DerefMut for devela::work::MutexGuard<'_, T>where
T: ?Sized,
impl<T> DerefMut for devela::work::RwLockWriteGuard<'_, T>where
T: ?Sized,
impl<T> DerefMut for ThinBox<T>where
T: ?Sized,
impl<T> DerefMut for PyRefMut<'_, T>where
T: PyClass<Frozen = False>,
impl<T> DerefMut for Seal<'_, T>
impl<T> DerefMut for Align<T>
impl<T> DerefMut for SerVec<T>
impl<T> DerefMut for Clamped<T>
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 CachePadded<T>
impl<T> DerefMut for Owned<T>where
T: Pointable + ?Sized,
impl<T> DerefMut for ShardedLockWriteGuard<'_, T>where
T: ?Sized,
impl<T, A> DerefMut for devela::all::Box<T, A>
impl<T, A> DerefMut for devela::all::Vec<T, A>where
A: Allocator,
impl<T, A> DerefMut for PeekMut<'_, T, A>
impl<T, A> DerefMut for UniqueRc<T, A>
impl<T, E> DerefMut for Strategy<T, E>where
T: ?Sized,
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, S> DerefMut for ScopeGuard<T, F, S>
impl<T, const CAP: usize> DerefMut for DstArray<T, CAP>
unsafe_layout only.