retainAll method
Returns a copy of this set where are all elements that are not in other
are removed from.
Checks for each element of other
whether there is an element in this set
that is equal to it (according to contains), and if so, the equal
element in this set is retained in the copy, and elements that are not
equal to any element in other
are removed from the copy.
Implementation
ImmortalSet<T> retainAll(ImmortalSet<Object?> other) =>
retainIterable(other.toSet());