Add entry_ref API to HashMap

[ajtribick]

An initial attempt at an entry_ref API to do the simple case that raw_entry_mut is used for. I basically attempted to mirror the existing entry API, but allow passing a borrowed version of the key. I left off mirroring the Send and Sync traits as I'm not sure what these should be.

The relationships I use between the key K and borrowed key Q is K: Borrow<Q> + From<&Q>. The reason for not using Q: ToOwned<K> is to support key types like Rc<str> (which is used in a couple of the doctests), which would not be possible with to_owned().

Hopefully this is somewhat useful.

[Amanieu]

Great work! I'm really glad to see this feature, it was much needed!

cc @rust-lang/libs-api since this API is likely to come to the standard library HashMap soon and I would like to iterate on the API within the hashbrown repo first.

[Amanieu]

KeyOrRef is a private type, so this method doesn't need to be pub.

[ajtribick]

Thanks, updated.

[ajtribick]

I'm not sure why the update triggered the clippy warning for missing safety docs on the Allocator trait when the first version did not. Presumably the safety docs should be something like the ones at https://doc.rust-lang.org/nightly/core/alloc/trait.Allocator.html ?

[Amanieu]

It's most likely because CI always uses the latest rust nightly and this lint was recently added to clippy.

I think you can safely just disable this lint. This Allocator trait isn't exposed outside this crate anyways.

[ajtribick]

Ok, lint is disabled. Regarding the Send and Sync implementations (presumably needed for OccupiedEntryRef), how should I implement these?

[Amanieu]

For Send: it requires that K,V,S,A are Send and that Q is Sync. This is because &T is Send if T: Sync.
For Sync: it requires that K,V,S,A,Q are `Sync.

[ajtribick]

Thanks! Added the impls.

[Amanieu]

@bors r+

[bors]

📌 Commit 7c545e1 has been approved by Amanieu

[bors]

⌛ Testing commit 7c545e1 with merge 898a9fe...

[bors]

☀️ Test successful - checks-actions
Approved by: Amanieu
Pushing 898a9fe to master...