mtls
only.Expand description
Used to do a cheap reference-to-reference conversion.
This trait is similar to AsMut
which is used for converting between mutable references.
If you need to do a costly conversion it is better to implement From
with type
&T
or write a custom function.
AsRef
has the same signature as Borrow
, but Borrow
is different in a few aspects:
- Unlike
AsRef
,Borrow
has a blanket impl for anyT
, and can be used to accept either a reference or a value. Borrow
also requires thatHash
,Eq
andOrd
for a borrowed value are equivalent to those of the owned value. For this reason, if you want to borrow only a single field of a struct you can implementAsRef
, but notBorrow
.
Note: This trait must not fail. If the conversion can fail, use a
dedicated method which returns an Option<T>
or a Result<T, E>
.
Generic Implementations
AsRef
auto-dereferences if the inner type is a reference or a mutable reference (e.g.:foo.as_ref()
will work the same iffoo
has type&mut Foo
or&&mut Foo
)
Examples
By using trait bounds we can accept arguments of different types as long as they can be
converted to the specified type T
.
For example: By creating a generic function that takes an AsRef<str>
we express that we
want to accept all references that can be converted to &str
as an argument.
Since both String
and &str
implement AsRef<str>
we can accept both as input argument.
fn is_hello<T: AsRef<str>>(s: T) {
assert_eq!("hello", s.as_ref());
}
let s = "hello";
is_hello(s);
let s = "hello".to_string();
is_hello(s);
Required Methods
Implementations on Foreign Types
const: unstable · sourceimpl<'_, T, U> AsRef<U> for &'_ mut T where
T: AsRef<U> + ?Sized,
U: ?Sized,
impl<'_, T, U> AsRef<U> for &'_ mut T where
T: AsRef<U> + ?Sized,
U: ?Sized,
sourceimpl<T, const LANES: usize> AsRef<[T; LANES]> for Simd<T, LANES> where
T: SimdElement,
LaneCount<LANES>: SupportedLaneCount,
impl<T, const LANES: usize> AsRef<[T; LANES]> for Simd<T, LANES> where
T: SimdElement,
LaneCount<LANES>: SupportedLaneCount,
sourceimpl<T, const LANES: usize> AsRef<[T]> for Simd<T, LANES> where
T: SimdElement,
LaneCount<LANES>: SupportedLaneCount,
impl<T, const LANES: usize> AsRef<[T]> for Simd<T, LANES> where
T: SimdElement,
LaneCount<LANES>: SupportedLaneCount,
sourceimpl AsRef<UnixStream> for OwnedReadHalf
impl AsRef<UnixStream> for OwnedReadHalf
fn as_ref(&self) -> &UnixStream
sourceimpl AsRef<UnixStream> for OwnedWriteHalf
impl AsRef<UnixStream> for OwnedWriteHalf
fn as_ref(&self) -> &UnixStream
sourceimpl<'_> AsRef<UnixStream> for ReadHalf<'_>
impl<'_> AsRef<UnixStream> for ReadHalf<'_>
fn as_ref(&self) -> &UnixStream
sourceimpl<'_> AsRef<UnixStream> for WriteHalf<'_>
impl<'_> AsRef<UnixStream> for WriteHalf<'_>
fn as_ref(&self) -> &UnixStream
sourceimpl<T> AsRef<UnboundedReceiver<T>> for UnboundedReceiverStream<T>
impl<T> AsRef<UnboundedReceiver<T>> for UnboundedReceiverStream<T>
fn as_ref(&self) -> &UnboundedReceiver<T>
sourceimpl<L, R> AsRef<OsStr> for Either<L, R> where
L: AsRef<OsStr>,
R: AsRef<OsStr>,
impl<L, R> AsRef<OsStr> for Either<L, R> where
L: AsRef<OsStr>,
R: AsRef<OsStr>,
Requires crate feature use_std
.
sourceimpl<L, R> AsRef<CStr> for Either<L, R> where
L: AsRef<CStr>,
R: AsRef<CStr>,
impl<L, R> AsRef<CStr> for Either<L, R> where
L: AsRef<CStr>,
R: AsRef<CStr>,
Requires crate feature use_std
.
sourceimpl<L, R> AsRef<Path> for Either<L, R> where
L: AsRef<Path>,
R: AsRef<Path>,
impl<L, R> AsRef<Path> for Either<L, R> where
L: AsRef<Path>,
R: AsRef<Path>,
Requires crate feature use_std
.