>>>>> "Bert" == Bert Freudenberg <bert at freudenbergs.de> writes:

Bert> I'd prefer (3d): make a class called UnoccupiedSlot, use it as marker
Bert> (either the class itself [I'd like that] or its singleton instance [for
Bert> the purists]). This would make it blatantly obvious what's happening
Bert> when inspecting the innards of a Set.

The problem with that is that you're simply moving the problem.

Now I can't have a Set of all classes. :(

That's the beauty of my "each set contains its own unique nil marker"
solution.  Any set can contain anything except its own insides, which is a
limitation that would only occur if you're doing something very very nasty.  A
set of all classes is far more likely to occur.

-- 
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