Return a reference providing modifiable access to the mapped value associated with the a key equivalent to the specified key in this map. If this map does not already contain an element eqivalent to key, insert an element with the KEY constructed from std::forward<LOOKUP_KEY>(k) and a default-constructed VALUE, and return a reference to the newly mapped value.
Declared in <bdlc_flathashmap.h>
template<class LOOKUP_KEY>
VALUE&
operator[](LOOKUP_KEY&& key)
requires BloombergLP::bslmf::IsTransparentPredicate<HASH, LOOKUP_KEY>::value
&& BloombergLP::bslmf::IsTransparentPredicate<EQUAL,LOOKUP_KEY>::value;