pub trait DerefMut: Deref {
// Required method
fn deref_mut(&mut self) -> &mut Self::Target;
}Available on crate features
crypto and 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§
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 syn::token::And
impl DerefMut for Asn1BitString
impl DerefMut for Asn1GeneralizedTime
impl DerefMut for Asn1Integer
impl DerefMut for Asn1Object
impl DerefMut for Asn1String
impl DerefMut for Asn1Time
impl DerefMut for syn::token::At
impl DerefMut for syn::token::At
impl DerefMut for Authority
impl DerefMut for BigNum
impl DerefMut for BigNumContext
impl DerefMut for BlockingClientWebSocket
impl DerefMut for Body
impl DerefMut for BorrowedPayload<'_>
impl DerefMut for ByteStr
impl DerefMut for ByteString
impl DerefMut for Bytes
impl DerefMut for BytesMut
impl DerefMut for syn::token::Caret
impl DerefMut for syn::token::Caret
impl DerefMut for CipherCtx
impl DerefMut for Client
impl DerefMut for rama::tls::rustls::dep::rustls::ClientConnection
impl DerefMut for rama::tls::rustls::dep::rustls::quic::ClientConnection
impl DerefMut for syn::token::Colon
impl DerefMut for syn::token::Colon
impl DerefMut for syn::token::Comma
impl DerefMut for syn::token::Comma
impl DerefMut for Conf
impl DerefMut for ConnectConfiguration
impl DerefMut for rama::tls::rustls::dep::rustls::Connection
impl DerefMut for rama::tls::rustls::dep::rustls::quic::Connection
impl DerefMut for Digest
impl DerefMut for DigestBytes
impl DerefMut for DnsRequest
impl DerefMut for DnsResponse
impl DerefMut for DocumentMut
impl DerefMut for syn::token::Dollar
impl DerefMut for syn::token::Dollar
impl DerefMut for syn::token::Dot
impl DerefMut for syn::token::Dot
impl DerefMut for EcGroup
impl DerefMut for EcPoint
impl DerefMut for EcdsaSig
impl DerefMut for syn::token::Eq
impl DerefMut for syn::token::Eq
impl DerefMut for Error
Available on crate feature
std or non-anyhow_no_core_error only.