It provides the operations described in the preceding requirements table for unique keys;
that is, an
unordered_set supports the
a_uniq operations in that table,
not the
a_eq operations
. For an
unordered_set<Key> the
key_type
and the
value_type are both
Key. The
iterator and
const_iterator types are both constant iterator types
. It is unspecified whether they are the same type
.