Return a const iterator to the first element of this set.
Declared in <bslstl_unorderedset.h>
unordered_set<KEY, HASH, EQUAL, ALLOCATOR>::const_iterator
cbegin() const noexcept;Return an iterator providing non-modifiable access to the first value_type object in the sequence of value_type objects maintained by this set, or the cend iterator if this set is empty.
const iterator to the first element, or cend() if empty