use Borrow;
/// Key equivalence trait.
///
/// This trait allows hash table lookup to be customized.
/// It has one blanket implementation that uses the regular `Borrow` solution,
/// just like `HashMap` and `BTreeMap` do, so that you can pass `&str` to lookup
/// into a map with `String` keys and so on.
///
/// # Contract
///
/// The implementor **must** hash like `K`, if it is hashable.