Trait core::convert::AsRef

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

See the book for a more detailed comparison.

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

fn as_ref(&self) -> &T

Performs the conversion.

Implementors

• impl<'a, T: ?Sized, U: ?Sized> AsRef<U> for &'a T where
    T: AsRef<U>, 
• impl<'a, T: ?Sized, U: ?Sized> AsRef<U> for &'a mut T where
    T: AsRef<U>, 
• impl<T> AsRef<[T]> for [T]
• impl AsRef<str> for str
• impl<T> AsRef<[T]> for [T; 0]
• impl<T> AsRef<[T]> for [T; 1]
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• impl<'a, T> AsRef<[T]> for Iter<'a, T>
• impl AsRef<[u8]> for str