Trait DerefMut

1.0.0 (const: unstable) · Source
pub 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 · Source

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

Mutably dereferences the value.

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impl DerefMut for rama::tls::rustls::dep::rustls::Connection

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impl DerefMut for rama::tls::rustls::dep::rustls::quic::Connection

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impl DerefMut for BytesMut

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impl DerefMut for RequestContextExt

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impl DerefMut for NameServerConfigGroup

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impl DerefMut for Forwarded

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impl DerefMut for Authority

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impl DerefMut for Body

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impl DerefMut for Bytes

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impl DerefMut for Host

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impl DerefMut for Text

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impl DerefMut for ClientWebSocket

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impl DerefMut for ServerWebSocket

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impl DerefMut for ClientSocketInfo

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impl DerefMut for Asn1BitString

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impl DerefMut for Asn1GeneralizedTime

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impl DerefMut for Asn1Integer

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impl DerefMut for Asn1Object

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impl DerefMut for Asn1String

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impl DerefMut for Asn1Time

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impl DerefMut for BigNum

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impl DerefMut for BigNumContext

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impl DerefMut for Conf

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impl DerefMut for EcGroup

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impl DerefMut for EcPoint

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impl DerefMut for EcdsaSig

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impl DerefMut for DigestBytes

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impl DerefMut for HpkeKey

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impl DerefMut for Pkcs12

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impl DerefMut for SrtpProtectionProfile

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impl DerefMut for ConnectConfiguration

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impl DerefMut for Ssl

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impl DerefMut for SslAcceptorBuilder

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impl DerefMut for SslCipher

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impl DerefMut for SslConnectorBuilder

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impl DerefMut for SslContext

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impl DerefMut for SslEchKeys

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impl DerefMut for SslSession

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impl DerefMut for OpensslString

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impl DerefMut for X509Store

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impl DerefMut for X509StoreBuilder

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impl DerefMut for GeneralName

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impl DerefMut for X509

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impl DerefMut for X509Algorithm

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impl DerefMut for X509Extension

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impl DerefMut for X509Name

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impl DerefMut for X509NameEntry

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impl DerefMut for X509Object

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impl DerefMut for X509Req

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impl DerefMut for X509StoreContext

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impl DerefMut for X509VerifyParam

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impl DerefMut for UnbufferedClientConnection

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impl DerefMut for BorrowedPayload<'_>

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impl DerefMut for rama::tls::rustls::dep::rustls::quic::ClientConnection

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impl DerefMut for rama::tls::rustls::dep::rustls::quic::ServerConnection

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impl DerefMut for UnbufferedServerConnection

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impl DerefMut for rama::tls::rustls::dep::rustls::ClientConnection

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impl DerefMut for rama::tls::rustls::dep::rustls::ServerConnection

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impl DerefMut for ClientUnixSocketInfo

1.3.0 · Source§

impl DerefMut for String

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impl DerefMut for ByteString

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impl DerefMut for ByteStr

1.44.0 · Source§

impl DerefMut for OsString

1.68.0 · Source§

impl DerefMut for PathBuf

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impl DerefMut for Digest

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impl DerefMut for DnsRequest

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impl DerefMut for DnsResponse

1.36.0 · Source§

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

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

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

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

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impl<'a, R, T> DerefMut for MappedRwLockWriteGuard<'a, R, T>
where R: RawRwLock + 'a, T: 'a + ?Sized,

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impl<'a, R, T> DerefMut for MutexGuard<'a, R, T>
where R: RawMutex + 'a, T: 'a + ?Sized,

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impl<'a, R, T> DerefMut for RwLockWriteGuard<'a, R, T>
where R: RawRwLock + 'a, T: 'a + ?Sized,

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impl<'a, T> DerefMut for rama::crypto::dep::x509_parser::prelude::asn1_rs::nom::lib::std::vec::PeekMut<'a, T>

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

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

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

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

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

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

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

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

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

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

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

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

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

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impl<C> DerefMut for Authorization<C>

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impl<C, ID> DerefMut for LeasedConnection<C, ID>

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impl<Data> DerefMut for rama::tls::rustls::dep::rustls::quic::ConnectionCommon<Data>

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

1.33.0 · Source§

impl<Ptr> DerefMut for Pin<Ptr>
where Ptr: DerefMut, <Ptr as Deref>::Target: Unpin,

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impl<R> DerefMut for RequestStatePair<R>

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

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impl<S> DerefMut for Ascii<S>

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impl<S> DerefMut for UniCase<S>

1.0.0 · Source§

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

1.0.0 (const: unstable) · Source§

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

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

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impl<T> DerefMut for rama::futures::lock::OwnedMutexGuard<T>
where T: ?Sized,

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impl<T> DerefMut for Csv<T>

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impl<T> DerefMut for Form<T>

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impl<T> DerefMut for Json<T>

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impl<T> DerefMut for Path<T>

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impl<T> DerefMut for AppendHeaders<T>

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impl<T> DerefMut for Css<T>

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impl<T> DerefMut for Html<T>

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impl<T> DerefMut for Script<T>

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impl<T> DerefMut for JsonEventData<T>

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impl<T> DerefMut for Dh<T>

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impl<T> DerefMut for Dsa<T>

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impl<T> DerefMut for EcKey<T>

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impl<T> DerefMut for PKey<T>

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impl<T> DerefMut for Rsa<T>

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impl<T> DerefMut for Stack<T>
where T: Stackable,

1.0.0 · Source§

impl<T> DerefMut for rama::tls::rustls::dep::rustls::lock::MutexGuard<'_, T>
where T: ?Sized,

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impl<T> DerefMut for rama::tls::rustls::dep::rustls::ConnectionCommon<T>

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impl<T> DerefMut for SequenceOf<T>

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impl<T> DerefMut for SetOf<T>

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

1.20.0 · Source§

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

1.0.0 · Source§

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

1.9.0 · Source§

impl<T> DerefMut for AssertUnwindSafe<T>

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

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

1.0.0 · Source§

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

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impl<T> DerefMut for CachePadded<T>

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

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

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

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

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

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

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

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

1.0.0 · Source§

impl<T, A> DerefMut for rama::crypto::dep::x509_parser::prelude::asn1_rs::nom::lib::std::boxed::Box<T, A>
where A: Allocator, T: ?Sized,

1.12.0 · Source§

impl<T, A> DerefMut for rama::crypto::dep::x509_parser::prelude::asn1_rs::nom::lib::std::collections::binary_heap::PeekMut<'_, T, A>
where T: Ord, A: Allocator,

1.0.0 · Source§

impl<T, A> DerefMut for rama::crypto::dep::x509_parser::prelude::asn1_rs::nom::lib::std::vec::Vec<T, A>
where A: Allocator,

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

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

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

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

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

1.89.0 · Source§

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

1.89.0 · Source§

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

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

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

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

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

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

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impl<T, U> DerefMut for OwnedMappedMutexGuard<T, U>
where T: ?Sized, U: ?Sized,

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impl<T, U> DerefMut for OwnedRwLockMappedWriteGuard<T, U>
where T: ?Sized, U: ?Sized,

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impl<Z> DerefMut for Zeroizing<Z>
where Z: Zeroize,