HashMap::get_key_value_mut?

[dodomorandi]

I found myself needing a partially mutable version of HashMap::get_key_value, with the following signature:

pub fn get_key_value_mut<Q: ?Sized>(&mut self, k: &Q) -> Option<(&K, &mut V)> where
    K: Borrow<Q>,
    Q: Hash + Eq, 

Obviously I was looking at std, and I think I cannot obtain nothing similar without the unstable hash_raw_entry API. However, hashbrown currently supports the API, therefore it should be pretty straightforward to implement the new feature.

The only thing I am still doubtful is the possibility of creating of an inconsistent state with the proposed API. At first glance, it should not be possible to smash the state of the hashmap, but maybe I am missing something. What do you think?

[Amanieu]

I think this is a reasonable addition to the API. I am happy to accept a PR for it.

[Amanieu]

Actually you can already do this with the existing API by using entry(), matching an OccupiedEntry and then calling key and get_mut.

[dodomorandi]

Actually you can already do this with the existing API by using entry(), matching an OccupiedEntry and then calling key and get_mut.

The issue with that, if I am not wrong, is that get_mut cannot be used because there is already a borrow of self for the call to key.

I think this is a reasonable addition to the API. I am happy to accept a PR for it.

Of course! I see that HashMap::get_key_value directly uses table.find with a bit of unsafe. It is ok if I follow the same approach?

[Amanieu]

The issue with that, if I am not wrong, is that get_mut cannot be used because there is already a borrow of self for the call to key.

Ah yes, I forgot about that.

Of course! I see that HashMap::get_key_value directly uses table.find with a bit of unsafe. It is ok if I follow the same approach?

Sure, that's fine.