Unfortunately, when preparing new finalization stuff, i got stuck with HashedCollection which is not yet integrated to Pharo. (Sets with nils also depending on that). In Squeak, old WeakRegistry does the trick by setting a #finalizer: to WeakKeyDictionary instance. Levente, can i ask you to give me a bits, (changesets or mcz packages), which contain HashedCollection refactorings. Or, we can follow an easier path, just extract the delta from two packages, which i found in mail archives: --- I uploaded two packages which contain this change. To load it evaluate the following: (Installer squeakfoundation project: 'inbox') install: 'Collections-ul.310.mcz'; install: 'Collections-ul.311.mcz' --- these are only related to WeakKeyDictionary, made by Levente to speedup old finalization. -- Best regards, Igor Stasenko AKA sig.