Adding Extend<&'a (K, V)> for HashMap<K, V, S, A>

[JustForFun88]

I think that it is strange that we can do something like this:

fn main() {
    use hashbrown::HashMap;
    let mut map = HashMap::new();
    let some_vec: Vec<_> = vec![(1, 1), (2, 2), (3, 3), (4, 4)];
    map.extend(some_vec.iter().map(|&(k, v)| (k, v)));
}

but cannot do something like this:

fn main() {
    use hashbrown::HashMap;
    let mut map = HashMap::new();
    let some_vec: Vec<_> = vec![(1, 1), (2, 2), (3, 3), (4, 4)];
    map.extend(some_vec.iter()); // Or map.extend(&some_vec);
}

In any case, it can work only if K and V are Copy, and also inside Extend<(K, V)> we use HashMap::insert, not HashMap::insert_unique_unchecked, so adding Extend<&'a (K, V)> should be Ok.

[Amanieu]

@bors r+

[bors]

📌 Commit bedc992 has been approved by Amanieu

[bors]

⌛ Testing commit bedc992 with merge 620cfc0...

[bors]

☀️ Test successful - checks-actions
Approved by: Amanieu
Pushing 620cfc0 to master...