Fix issue #11216 - Replace std::hashmap::{each_key, each_value} with iterators

[Dretch]

No description provided.

[alexcrichton]

I think you can actually avoid making two new structures as well::

type HashMapKeyIterator<'a, K, V> = Map<'static, (&'a K, &'a V), &'a V, HashMapIterator<'a, K, V>>;

pub fn keys<'a>(&'a self) -> HashMapKeyIterator<'a, K, V> {           
    self.iter().map(|(_, v)| v)                                         
}                                                                       

A little wordy on the type definition, but it gets the job done!

[alexcrichton]

Two more minor things, then this is good to go:

• Could you make the type definitions pub type so external callers can use them?
• Could you squash these into one commit?

Thanks!

[Dretch]

@alexcrichton

I have implemented your requests. r?

[alexcrichton]

Thanks, and nice work!