Trait std::convert::AsRef

pub trait AsRef<T> where
    T: ?Sized, {
    fn as_ref(&self) -> &T;
}

A cheap reference-to-reference conversion. Used to convert a value to a reference value within generic code.

AsRef is very similar to, but serves a slightly different purpose than, Borrow.

AsRef is to be used when wishing to convert to a reference of another type. Borrow is more related to the notion of taking the reference. It is useful when wishing to abstract over the type of reference (&T, &mut T) or allow both the referenced and owned type to be treated in the same manner.

The key difference between the two traits is the intention:

• Use AsRef when the goal is to simply convert into a reference
• Use Borrow when the goal is related to writing code that is agnostic to the type of borrow and whether it is a reference or value

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 if foo has type &mut Foo or &&mut Foo)

Examples

Both String and &str implement AsRef<str>:

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

Important traits for &'_ mut I

impl<'_, I> Iterator for &'_ mut I where
    I: Iterator + ?Sized,  type Item = <I as Iterator>::Item;impl<'_, F> Future for &'_ mut F where
    F: Unpin + Future + ?Sized,  type Output = <F as Future>::Output;impl<R: Read + ?Sized, '_> Read for &'_ mut Rimpl<W: Write + ?Sized, '_> Write for &'_ mut W

fn as_ref(&self) -> &T

Performs the conversion.

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Implementors

impl AsRef<[u8]> for str

Important traits for &'_ [u8]

impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]

fn as_ref(&self) -> &[u8]

impl AsRef<[u8]> for String

Important traits for &'_ [u8]

impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]

fn as_ref(&self) -> &[u8]

impl AsRef<str> for str

fn as_ref(&self) -> &str

impl AsRef<str> for String

fn as_ref(&self) -> &str

impl AsRef<CStr> for CStr

fn as_ref(&self) -> &CStr

impl AsRef<CStr> for CString

fn as_ref(&self) -> &CStr

impl AsRef<OsStr> for str

fn as_ref(&self) -> &OsStr

impl AsRef<OsStr> for OsStr

fn as_ref(&self) -> &OsStr

impl AsRef<OsStr> for OsString

fn as_ref(&self) -> &OsStr

impl AsRef<OsStr> for Path

fn as_ref(&self) -> &OsStr

impl AsRef<OsStr> for PathBuf

fn as_ref(&self) -> &OsStr

impl AsRef<OsStr> for String

fn as_ref(&self) -> &OsStr

impl AsRef<Path> for str

fn as_ref(&self) -> &Path

impl AsRef<Path> for OsStr

fn as_ref(&self) -> &Path

impl AsRef<Path> for OsString

fn as_ref(&self) -> &Path

impl AsRef<Path> for Path

fn as_ref(&self) -> &Path

impl AsRef<Path> for PathBuf

fn as_ref(&self) -> &Path

impl AsRef<Path> for String

fn as_ref(&self) -> &Path

impl<'_> AsRef<OsStr> for Component<'_>

fn as_ref(&self) -> &OsStr

impl<'_> AsRef<OsStr> for Components<'_>

fn as_ref(&self) -> &OsStr

impl<'_> AsRef<OsStr> for std::path::Iter<'_>

fn as_ref(&self) -> &OsStr

impl<'_> AsRef<Path> for Cow<'_, OsStr>

fn as_ref(&self) -> &Path

impl<'_> AsRef<Path> for Component<'_>

fn as_ref(&self) -> &Path

impl<'_> AsRef<Path> for Components<'_>

fn as_ref(&self) -> &Path

impl<'_> AsRef<Path> for std::path::Iter<'_>

fn as_ref(&self) -> &Path

impl<'_, T> AsRef<[T]> for std::slice::Iter<'_, T>

Important traits for &'_ [u8]

impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]

fn as_ref(&self) -> &[T]

impl<'_, T> AsRef<T> for Cow<'_, T> where
    T: ToOwned + ?Sized, 

Important traits for &'_ mut I

impl<'_, I> Iterator for &'_ mut I where
    I: Iterator + ?Sized,  type Item = <I as Iterator>::Item;impl<'_, F> Future for &'_ mut F where
    F: Unpin + Future + ?Sized,  type Output = <F as Future>::Output;impl<R: Read + ?Sized, '_> Read for &'_ mut Rimpl<W: Write + ?Sized, '_> Write for &'_ mut W

fn as_ref(&self) -> &T

impl<'_, T, U> AsRef<U> for &'_ T where
    T: AsRef<U> + ?Sized,
    U: ?Sized, 

Important traits for &'_ mut I

impl<'_, I> Iterator for &'_ mut I where
    I: Iterator + ?Sized,  type Item = <I as Iterator>::Item;impl<'_, F> Future for &'_ mut F where
    F: Unpin + Future + ?Sized,  type Output = <F as Future>::Output;impl<R: Read + ?Sized, '_> Read for &'_ mut Rimpl<W: Write + ?Sized, '_> Write for &'_ mut W

fn as_ref(&self) -> &U

impl<'_, T, U> AsRef<U> for &'_ mut T where
    T: AsRef<U> + ?Sized,
    U: ?Sized, 

Important traits for &'_ mut I

impl<'_, I> Iterator for &'_ mut I where
    I: Iterator + ?Sized,  type Item = <I as Iterator>::Item;impl<'_, F> Future for &'_ mut F where
    F: Unpin + Future + ?Sized,  type Output = <F as Future>::Output;impl<R: Read + ?Sized, '_> Read for &'_ mut Rimpl<W: Write + ?Sized, '_> Write for &'_ mut W

fn as_ref(&self) -> &U

impl<T> AsRef<[T]> for [T; 0]

Important traits for &'_ [u8]

impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]

fn as_ref(&self) -> &[T]

impl<T> AsRef<[T]> for [T; 1]

Important traits for &'_ [u8]

impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]

fn as_ref(&self) -> &[T]

impl<T> AsRef<[T]> for [T; 2]

Important traits for &'_ [u8]

impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]

fn as_ref(&self) -> &[T]

impl<T> AsRef<[T]> for [T; 3]

Important traits for &'_ [u8]

impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]

fn as_ref(&self) -> &[T]

impl<T> AsRef<[T]> for [T; 4]

Important traits for &'_ [u8]

impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]

fn as_ref(&self) -> &[T]

impl<T> AsRef<[T]> for [T; 5]

Important traits for &'_ [u8]

impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]

fn as_ref(&self) -> &[T]

impl<T> AsRef<[T]> for [T; 6]

Important traits for &'_ [u8]

impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]

fn as_ref(&self) -> &[T]

impl<T> AsRef<[T]> for [T; 7]

Important traits for &'_ [u8]

impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]

fn as_ref(&self) -> &[T]

impl<T> AsRef<[T]> for [T; 8]

Important traits for &'_ [u8]

impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]

fn as_ref(&self) -> &[T]

impl<T> AsRef<[T]> for [T; 9]

Important traits for &'_ [u8]

impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]

fn as_ref(&self) -> &[T]

impl<T> AsRef<[T]> for [T; 10]

Important traits for &'_ [u8]

impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]

fn as_ref(&self) -> &[T]

impl<T> AsRef<[T]> for [T; 11]

Important traits for &'_ [u8]

impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]

fn as_ref(&self) -> &[T]

impl<T> AsRef<[T]> for [T; 12]

Important traits for &'_ [u8]

impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]

fn as_ref(&self) -> &[T]

impl<T> AsRef<[T]> for [T; 13]

Important traits for &'_ [u8]

impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]

fn as_ref(&self) -> &[T]

impl<T> AsRef<[T]> for [T; 14]

Important traits for &'_ [u8]

impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]

fn as_ref(&self) -> &[T]

impl<T> AsRef<[T]> for [T; 15]

Important traits for &'_ [u8]

impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]

fn as_ref(&self) -> &[T]

impl<T> AsRef<[T]> for [T; 16]

Important traits for &'_ [u8]

impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]

fn as_ref(&self) -> &[T]

impl<T> AsRef<[T]> for [T; 17]

Important traits for &'_ [u8]

impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]

fn as_ref(&self) -> &[T]

impl<T> AsRef<[T]> for [T; 18]

Important traits for &'_ [u8]

impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]

fn as_ref(&self) -> &[T]

impl<T> AsRef<[T]> for [T; 19]

Important traits for &'_ [u8]

impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]

fn as_ref(&self) -> &[T]

impl<T> AsRef<[T]> for [T; 20]

Important traits for &'_ [u8]

impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]

fn as_ref(&self) -> &[T]

impl<T> AsRef<[T]> for [T; 21]

Important traits for &'_ [u8]

impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]

fn as_ref(&self) -> &[T]

impl<T> AsRef<[T]> for [T; 22]

Important traits for &'_ [u8]

impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]

fn as_ref(&self) -> &[T]

impl<T> AsRef<[T]> for [T; 23]

Important traits for &'_ [u8]

impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]

fn as_ref(&self) -> &[T]

impl<T> AsRef<[T]> for [T; 24]

Important traits for &'_ [u8]

impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]

fn as_ref(&self) -> &[T]

impl<T> AsRef<[T]> for [T; 25]

Important traits for &'_ [u8]

impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]

fn as_ref(&self) -> &[T]

impl<T> AsRef<[T]> for [T; 26]

Important traits for &'_ [u8]

impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]

fn as_ref(&self) -> &[T]

impl<T> AsRef<[T]> for [T; 27]

Important traits for &'_ [u8]

impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]

fn as_ref(&self) -> &[T]

impl<T> AsRef<[T]> for [T; 28]

Important traits for &'_ [u8]

impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]

fn as_ref(&self) -> &[T]

impl<T> AsRef<[T]> for [T; 29]

Important traits for &'_ [u8]

impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]

fn as_ref(&self) -> &[T]

impl<T> AsRef<[T]> for [T; 30]

Important traits for &'_ [u8]

impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]

fn as_ref(&self) -> &[T]

impl<T> AsRef<[T]> for [T; 31]

Important traits for &'_ [u8]

impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]

fn as_ref(&self) -> &[T]

impl<T> AsRef<[T]> for [T; 32]

Important traits for &'_ [u8]

impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]

fn as_ref(&self) -> &[T]

impl<T> AsRef<[T]> for [T]

Important traits for &'_ [u8]

impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]

fn as_ref(&self) -> &[T]

impl<T> AsRef<[T]> for Vec<T>

Important traits for &'_ [u8]

impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]

fn as_ref(&self) -> &[T]

impl<T> AsRef<Vec<T>> for Vec<T>

Important traits for Vec<u8>

impl Write for Vec<u8>

fn as_ref(&self) -> &Vec<T>

impl<T> AsRef<T> for Box<T> where
    T: ?Sized, 

Important traits for &'_ mut I

impl<'_, I> Iterator for &'_ mut I where
    I: Iterator + ?Sized,  type Item = <I as Iterator>::Item;impl<'_, F> Future for &'_ mut F where
    F: Unpin + Future + ?Sized,  type Output = <F as Future>::Output;impl<R: Read + ?Sized, '_> Read for &'_ mut Rimpl<W: Write + ?Sized, '_> Write for &'_ mut W

fn as_ref(&self) -> &T

impl<T> AsRef<T> for Rc<T> where
    T: ?Sized, 

Important traits for &'_ mut I

impl<'_, I> Iterator for &'_ mut I where
    I: Iterator + ?Sized,  type Item = <I as Iterator>::Item;impl<'_, F> Future for &'_ mut F where
    F: Unpin + Future + ?Sized,  type Output = <F as Future>::Output;impl<R: Read + ?Sized, '_> Read for &'_ mut Rimpl<W: Write + ?Sized, '_> Write for &'_ mut W

fn as_ref(&self) -> &T

impl<T> AsRef<T> for Arc<T> where
    T: ?Sized, 

Important traits for &'_ mut I

impl<'_, I> Iterator for &'_ mut I where
    I: Iterator + ?Sized,  type Item = <I as Iterator>::Item;impl<'_, F> Future for &'_ mut F where
    F: Unpin + Future + ?Sized,  type Output = <F as Future>::Output;impl<R: Read + ?Sized, '_> Read for &'_ mut Rimpl<W: Write + ?Sized, '_> Write for &'_ mut W

fn as_ref(&self) -> &T

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