I imagine you are referencing this comment "One could make WeakSet implementations that are iterable, but those can lead to non-deterministic algorithms (depend

I imagine you are referencing this comment "One could make WeakSet implementations that are iterable, but those can lead to non-deterministic algorithms (depending on GC behaviour) if used in the wrong way, and therefore the ES committee decided not to make the contents available." I suppose when I said "you've now created a really tricky situation where iteration essentially forces a GC pass because it needs to know whats reachable and what isn't at iteration time", I was directly responding to this behavior: if you have a GC pass before every iteration, it clearly would solve the non-determinism problem, as you would have an iteration that had well-defined behavior. I took it as a given that an iteration that sometimes returns things with no external references and sometimes doesn't would be completely absurd, and thus the GC pass would be required. If you are telling me that this is precisely how Java's works however, then I guess I should have known better and checked that a language like Java apparently does allow this ... interesting behavior. (I certainly don't know how it works there)