They do because the standard library implementation was changed to use Hashbrown. However the standard library API has a slight limitation in that you can't get say "I have a reference to a string. If there's an entry for it, give me that. Otherwise clone the string and insert a new entry. Also only do one key lookup."

You end up either having to do two lookups or always cloning the string even if you ended up not needing it.

You can.

https://doc.rust-lang.org/std/collections/hash_map/enum.Entr...

You can't. `entry()` takes they key by value, not by reference:

https://doc.rust-lang.org/std/collections/hash_map/struct.Ha...

You might be getting confused because in that example the `HashMap` keys are references.

My bad. That’s not been an issue in my code, as I use arenas to manage memory and never put an owning container as key in a HashMap.