Where is CountedSet in Swift 3 (beta 6)?

Question

Swift 3 introduces the CountedSet class (yes it's a class, not a struct) which should replace/bridge the old Objective-C NSCountedSet class.

However using the last beta of Swift 3 (beta 6) the CountedSet symbol is no longer recognised. What happened to it?

Answer 1

Based on this proposal, CountedSet has been considered and rejected or deferred.

The following classes were considered and rejected or deferred for the described reasons:

OrderedSet, CountedSet: We will consider these types in a future proposal.