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 few aspects:

• Unlike 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>.

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

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

Important traits for &'_ mut F

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 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 F

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 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 F

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 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 F

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 Rimpl<'_, W: Write + ?Sized> Write for &'_ mut W

fn as_ref(&self) -> &U

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 F

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 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 F

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 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 F

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 Rimpl<'_, W: Write + ?Sized> Write for &'_ mut W

fn as_ref(&self) -> &T

impl<const N: usize, T> AsRef<[T]> for [T; N] where
    [T; N]: LengthAtMost32, 

Important traits for &'_ [u8]

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

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

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