kvarn_async::prelude::compact_str::core::convert

Trait AsRef

1.6.0 · source 
pub trait AsRef<T>
where
    T: ?Sized,
{
    // Required method
    fn as_ref(&self) -> &T;
}
Expand description

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.

§Relation to Borrow

AsRef has the same signature as Borrow, but Borrow is different in a few aspects:

  • Unlike AsRef, Borrow has a blanket impl for any T, and can be used to accept either a reference or a value. (See also note on AsRef’s reflexibility below.)
  • Borrow also requires that Hash, Eq and Ord 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 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).

Note that due to historic reasons, the above currently does not hold generally for all dereferenceable types, e.g. foo.as_ref() will not work the same as Box::new(foo).as_ref(). Instead, many smart pointers provide an as_ref implementation which simply returns a reference to the pointed-to value (but do not perform a cheap reference-to-reference conversion for that value). However, AsRef::as_ref should not be used for the s