Return an iterator to the first element, or end if empty.
Declared in <bslstl_unorderedmultiset.h>
unordered_multiset<KEY, HASH, EQUAL, ALLOCATOR>::iterator
begin() noexcept;
Return an iterator providing modifiable access to the first value_type object (in the sequence of value_type objects) maintained by this unordered multiset, or the end iterator if this unordered multiset is empty.
iterator to the first element, or end() if empty