Return true if this unordered multiset contains an element whose key is equivalent to the specified key.
Declared in <bslstl_unorderedmultiset.h>
template<class LOOKUP_KEY>
bool
contains(LOOKUP_KEY const& key) const
requires BloombergLP::bslmf::IsTransparentPredicate<HASH, LOOKUP_KEY>::value &&
BloombergLP::bslmf::IsTransparentPredicate<EQUAL,
LOOKUP_KEY>::value;