pub trait DerefMut: Deref {
// Required method
fn deref_mut(&mut self) -> &mut Self::Target;
}
mtls
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
‘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.
Violating these requirements is a logic error. The behavior resulting from a logic error is not
specified, but users of the trait must ensure that such logic errors do not result in
undefined behavior. This means that unsafe
code must not rely on the correctness of this
method.
More on Deref
coercion
If T
implements DerefMut<Target = U>
, and x
is a value of type T
,
then:
- In mutable contexts,
*x
(whereT
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 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.
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 NamedFile
impl DerefMut for String
impl DerefMut for OsString
impl DerefMut for PathBuf
impl DerefMut for BytesMut
impl DerefMut for ClientConnection
impl DerefMut for Connection
impl DerefMut for Document
impl DerefMut for InlinableString
impl DerefMut for InlineString
impl DerefMut for ServerConnection
impl<'a> DerefMut for IoSliceMut<'a>
impl<'a> DerefMut for socket2::MaybeUninitSlice<'a>
impl<'a> DerefMut for MaybeUninitSlice<'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 tokio::sync::mutex::MappedMutexGuard<'a, T>where T: ?Sized,
impl<'a, T> DerefMut for MutexGuard<'a, T>where T: ?Sized,
impl<'a, T> DerefMut for MutexGuard<'a, T>where T: ?Sized,
impl<'a, T> DerefMut for SpinMutexGuard<'a, T>where T: ?Sized,
impl<'c> DerefMut for rocket::local::asynchronous::LocalRequest<'c>
impl<'c> DerefMut for rocket::local::blocking::LocalRequest<'c>
impl<'rwlock, T> DerefMut for RwLockWriteGuard<'rwlock, T>where T: ?Sized,
impl<'rwlock, T, R> DerefMut for RwLockWriteGuard<'rwlock, T, R>where T: ?Sized,
impl<'v> DerefMut for Errors<'v>
impl<A> DerefMut for SmallVec<A>where A: Array,
impl<B, T> DerefMut for Ref<B, [T]>where B: ByteSliceMut, T: FromBytes + AsBytes,
impl<B, T> DerefMut for Ref<B, T>where B: ByteSliceMut, T: FromBytes + AsBytes,
impl<I> DerefMut for Pear<I>where I: Input,
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> DerefMut for Pin<P>where P: DerefMut, <P as Deref>::Target: Unpin,
impl<T> !DerefMut for &Twhere T: ?Sized,
impl<T> DerefMut for &mut Twhere T: ?Sized,
impl<T> DerefMut for Capped<T>
impl<T> DerefMut for Form<T>
impl<T> DerefMut for Lenient<T>
impl<T> DerefMut for Strict<T>
impl<T> DerefMut for Json<T>
json
only.impl<T> DerefMut for MsgPack<T>
msgpack
only.