C++ associative containers - why doesn't the standard defines methods to exchange and replaces keys?

Question

I need to replace specific key values, while the rest of the value_type is left untouched. What I actually need to do, is copy the value, erase the entry and insert it with changed key value again. This is absolutely bad. I need to copy the whole value_type twice, and deallocate/allocate again.

Why the standard doesn't define methods like this:

// returns count of exchanged keys
size_type exchange_key(key_type const& x, key_type const& y);
// returns count of replaced keys
size_type replace_key(key_type const& old_key, key_type const& new_key);

Is there anything I'm missing?

Answer 1

Now, you can, with .extract(key) (since C++17). https://en.cppreference.com/w/cpp/container/map/extract