map::OccupiedEntryRef::key should return &K rather than &Q #421
Description
returning Q unnecessarily throws away the key type, which may have extra information needed by the user, e.g. the Rc you want to clone.
example where returning K is useful:
struct Interner<T: Eq + Hash> {
values: HashMap<Rc<T>, ()>,
}
impl<T: Eq + Hash> Interner<T>
where
Rc<T>: for<'a> From<&'a T>,
{
fn intern(&mut self, v: &T) -> Rc<T> {
match self.values.entry_ref(v) {
EntryRef::Occupied(entry) => Rc::clone(entry.key()), // getting `&Rc<T>` instead of `&T` avoids allocating a new `Rc<T>`
EntryRef::Vacant(entry) => Rc::clone(entry.insert_entry(()).key())
}
}
}