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 few aspects:
AsRef
, Borrow
has a blanket impl for any T
, and can be used to accept either a reference or a value.Borrow
also requires that Hash
, Eq
and Ord
for 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 implement AsRef
, but not Borrow
.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>
.
AsRef
auto-dereferences if the inner type is a reference or a mutable reference (e.g.: foo.as_ref()
will work the same if foo
has type &mut Foo
or &&mut Foo
)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);
fn as_ref(&self) -> &T
impl<'_, F> Future for &'_ mut F where F: Unpin + Future + ?Sized, type Output = <F as Future>::Output; impl<'_, I> Iterator for &'_ mut I where I: Iterator + ?Sized, type Item = <I as Iterator>::Item; impl<'_, R: Read + ?Sized> Read for &'_ mut R impl<'_, W: Write + ?Sized> Write for &'_ mut W
Performs the conversion.
impl AsRef<[u8]> for str
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impl AsRef<[u8]> for String
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impl AsRef<str> for str
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impl AsRef<str> for String
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impl AsRef<CStr> for CStr
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impl AsRef<CStr> for CString
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impl AsRef<OsStr> for str
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impl AsRef<OsStr> for OsStr
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impl AsRef<OsStr> for OsString
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impl AsRef<OsStr> for Path
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impl AsRef<OsStr> for PathBuf
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impl AsRef<OsStr> for String
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impl AsRef<Path> for str
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impl AsRef<Path> for OsStr
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impl AsRef<Path> for OsString
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impl AsRef<Path> for Path
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impl AsRef<Path> for PathBuf
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impl AsRef<Path> for String
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impl<'_> AsRef<OsStr> for Component<'_>
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impl<'_> AsRef<OsStr> for Components<'_>
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impl<'_> AsRef<OsStr> for std::path::Iter<'_>
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impl<'_> AsRef<Path> for Cow<'_, OsStr>
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impl<'_> AsRef<Path> for Component<'_>
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impl<'_> AsRef<Path> for Components<'_>
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impl<'_> AsRef<Path> for std::path::Iter<'_>
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impl<'_, T> AsRef<[T]> for std::slice::Iter<'_, T>
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impl<'_, T> AsRef<T> for Cow<'_, T> where
T: ToOwned + ?Sized,
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fn as_ref(&self) -> &T
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impl<'_, F> Future for &'_ mut F where F: Unpin + Future + ?Sized, type Output = <F as Future>::Output; impl<'_, I> Iterator for &'_ mut I where I: Iterator + ?Sized, type Item = <I as Iterator>::Item; impl<'_, R: Read + ?Sized> Read for &'_ mut R impl<'_, W: Write + ?Sized> Write for &'_ mut W
impl<'_, T, U> AsRef<U> for &'_ T where
T: AsRef<U> + ?Sized,
U: ?Sized,
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fn as_ref(&self) -> &U
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impl<'_, F> Future for &'_ mut F where F: Unpin + Future + ?Sized, type Output = <F as Future>::Output; impl<'_, I> Iterator for &'_ mut I where I: Iterator + ?Sized, type Item = <I as Iterator>::Item; impl<'_, R: Read + ?Sized> Read for &'_ mut R impl<'_, W: Write + ?Sized> Write for &'_ mut W
impl<'_, T, U> AsRef<U> for &'_ mut T where
T: AsRef<U> + ?Sized,
U: ?Sized,
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fn as_ref(&self) -> &U
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impl<'_, F> Future for &'_ mut F where F: Unpin + Future + ?Sized, type Output = <F as Future>::Output; impl<'_, I> Iterator for &'_ mut I where I: Iterator + ?Sized, type Item = <I as Iterator>::Item; impl<'_, R: Read + ?Sized> Read for &'_ mut R impl<'_, W: Write + ?Sized> Write for &'_ mut W
impl<T> AsRef<[T]> for [T; 0]
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impl<T> AsRef<[T]> for [T; 1]
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impl<T> AsRef<[T]> for [T; 2]
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impl<T> AsRef<[T]> for [T; 3]
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impl<T> AsRef<[T]> for [T; 4]
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impl<T> AsRef<[T]> for [T; 5]
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impl<T> AsRef<[T]> for [T; 6]
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impl<T> AsRef<[T]> for [T; 7]
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impl<T> AsRef<[T]> for [T; 8]
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impl<T> AsRef<[T]> for [T; 9]
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impl<T> AsRef<[T]> for [T; 10]
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impl<T> AsRef<[T]> for [T; 11]
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impl<T> AsRef<[T]> for [T; 12]
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impl<T> AsRef<[T]> for [T; 13]
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impl<T> AsRef<[T]> for [T; 14]
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impl<T> AsRef<[T]> for [T; 15]
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impl<T> AsRef<[T]> for [T; 16]
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impl<T> AsRef<[T]> for [T; 17]
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impl<T> AsRef<[T]> for [T; 18]
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impl<T> AsRef<[T]> for [T; 19]
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impl<T> AsRef<[T]> for [T; 20]
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impl<T> AsRef<[T]> for [T; 21]
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impl<T> AsRef<[T]> for [T; 22]
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impl<T> AsRef<[T]> for [T; 23]
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impl<T> AsRef<[T]> for [T; 24]
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impl<T> AsRef<[T]> for [T; 25]
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impl<T> AsRef<[T]> for [T; 26]
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impl<T> AsRef<[T]> for [T; 27]
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impl<T> AsRef<[T]> for [T; 28]
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impl<T> AsRef<[T]> for [T; 29]
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impl<T> AsRef<[T]> for [T; 30]
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impl<T> AsRef<[T]> for [T; 31]
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impl<T> AsRef<[T]> for [T; 32]
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impl<T> AsRef<[T]> for [T]
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impl<T> AsRef<[T]> for Vec<T>
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impl<T> AsRef<Vec<T>> for Vec<T>
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impl<T> AsRef<T> for Box<T> where
T: ?Sized,
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fn as_ref(&self) -> &T
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impl<'_, F> Future for &'_ mut F where F: Unpin + Future + ?Sized, type Output = <F as Future>::Output; impl<'_, I> Iterator for &'_ mut I where I: Iterator + ?Sized, type Item = <I as Iterator>::Item; impl<'_, R: Read + ?Sized> Read for &'_ mut R impl<'_, W: Write + ?Sized> Write for &'_ mut W
impl<T> AsRef<T> for Rc<T> where
T: ?Sized,
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fn as_ref(&self) -> &T
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impl<'_, F> Future for &'_ mut F where F: Unpin + Future + ?Sized, type Output = <F as Future>::Output; impl<'_, I> Iterator for &'_ mut I where I: Iterator + ?Sized, type Item = <I as Iterator>::Item; impl<'_, R: Read + ?Sized> Read for &'_ mut R impl<'_, W: Write + ?Sized> Write for &'_ mut W
impl<T> AsRef<T> for Arc<T> where
T: ?Sized,
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fn as_ref(&self) -> &T
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impl<'_, F> Future for &'_ mut F where F: Unpin + Future + ?Sized, type Output = <F as Future>::Output; impl<'_, I> Iterator for &'_ mut I where I: Iterator + ?Sized, type Item = <I as Iterator>::Item; impl<'_, R: Read + ?Sized> Read for &'_ mut R impl<'_, W: Write + ?Sized> Write for &'_ mut W
© 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