Insert into this unordered set a newly created value_type object, constructed by forwarding get_allocator() (if required) and the specified (variable number of) arguments to the corresponding constructor of value_type, if a key equivalent to such a value does not already exists in this set; otherwise, this method has no effect (other than possibly creating a temporary value_type object). Return an iterator referring to the (possibly newly created and inserted) object in this set whose value is equivalent to that of an object constructed from arguments. The average and worst case complexity of this operation is not affected by the specified hint. This method requires that the (template parameter) type KEY be emplace-constructible into this set from arguments (see {Requirements on KEY}). The behavior is undefined unless hint is an iterator in the range [begin() .. end()] (both endpoints included). Note that hint is ignored (other than possibly asserting its validity in some build modes).
Declared in <bslstl_unorderedset.h>
template<class... Args>
unordered_set<KEY, HASH, EQUAL, ALLOCATOR>::iterator
emplace_hint(
const_iterator hint,
Args&&... arguments);