If this map contains an entry with a key equivalent to the specified key, assign the specified obj to the mapped_type of that entry, and return an iterator to that entry and false. Otherwise, insert a new entry into the map with the and return an iterator to that entry and true. obj is left in a (valid) unspecified state.
Declared in <bdlc_flathashmap.h>
template<class M>
bsl::pair<FlatHashMap<KEY, VALUE, HASH, EQUAL>::iterator, bool>
insert_or_assign(
BloombergLP::bslmf::MovableRef<KEY> key,
M&& obj);