Trait std::convert::AsRef
pub trait AsRef<T> where T: ?Sized, { fn as_ref(&self) -> &T; }
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
fn as_ref(&self) -> &T
Converts this type into a shared reference of the (usually inferred) input type.
Implementations on Foreign Types
impl AsRef<CStr> for CStr
fn as_ref(&self) -> &CStr
impl AsRef<CStr> for CString
fn as_ref(&self) -> &CStr
Implementors
impl AsRef<[u8]> for str
impl AsRef<[u8]> for String
impl AsRef<str> for str
impl AsRef<str> for String
impl AsRef<OsStr> for Component<'_>
impl AsRef<OsStr> for str
impl AsRef<OsStr> for OsStr
impl AsRef<OsStr> for OsString
impl AsRef<OsStr> for Components<'_>
impl AsRef<OsStr> for std::path::Iter<'_>
impl AsRef<OsStr> for Path
impl AsRef<OsStr> for PathBuf
impl AsRef<OsStr> for String
impl AsRef<Path> for Cow<'_, OsStr>
impl AsRef<Path> for Component<'_>
impl AsRef<Path> for str
impl AsRef<Path> for OsStr
impl AsRef<Path> for OsString
impl AsRef<Path> for Components<'_>
impl AsRef<Path> for std::path::Iter<'_>
impl AsRef<Path> for Path
impl AsRef<Path> for PathBuf
impl AsRef<Path> for String
impl<'_, T> AsRef<[T]> for std::slice::Iter<'_, T>
impl<'_, T> AsRef<[T]> for IterMut<'_, T>
impl<'_, T> AsRef<T> for Cow<'_, T> where
T: ToOwned + ?Sized,
impl<'_, T, U> AsRef<U> for &'_ T where
T: AsRef<U> + ?Sized,
U: ?Sized,
impl<'_, T, U> AsRef<U> for &'_ mut T where
T: AsRef<U> + ?Sized,
U: ?Sized,
impl<'a> AsRef<[u8]> for std::string::Drain<'a>
impl<'a> AsRef<str> for std::string::Drain<'a>
impl<'a, T, A> AsRef<[T]> for std::vec::Drain<'a, T, A> where
A: Allocator,
impl<T> AsRef<[T]> for [T]
impl<T> AsRef<T> for Rc<T> where
T: ?Sized,
impl<T> AsRef<T> for Arc<T> where
T: ?Sized,
impl<T, A> AsRef<[T]> for IntoIter<T, A> where
A: Allocator,
impl<T, A> AsRef<[T]> for Vec<T, A> where
A: Allocator,
impl<T, A> AsRef<Vec<T, A>> for Vec<T, A> where
A: Allocator,
impl<T, A> AsRef<T> for Box<T, A> where
A: Allocator,
T: ?Sized,
impl<T, const LANES: usize> AsRef<[T; LANES]> 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,
impl<T, const N: usize> AsRef<[T]> for [T; N]
© 2010 The Rust Project Developers
Licensed under the Apache License, Version 2.0 or the MIT license, at your option.
https://doc.rust-lang.org/std/convert/trait.AsRef.html