bsl::map::insert_or_assign

If a key equivalent to the specified key already exists in this map, assign the specified obj to the value associated with that key, and return a pair containing an iterator referring to the existing item and false. Otherwise, insert into this map a newly‐created value_type object, constructed from (key, std::forward<BDE_OTHER_TYPE>(obj)...)), and return a pair containing an iterator referring to the newly‐created entry and true.