Hi all Phil: I'm sorry, didn't get what you point with the code snippet. The copy of the Symbol is the same instance, that I think it's nto GCed. Guille: Yes, I knew the internals of the WeakValueDictionary but asked about the API. What I don't know is about using WeakRegistry and Ephemerons. I'll check WeakKeyDictionary. I understand the idea of "explicit control of magic", but not sure if I understand concretely. Do you mean to implement something like WeakValueDictionary>>register which will not be executed by #initialize, so the user can decide to register. Am I right? Denis: +1 WeakSet behavior is really confusing! In thte case of WeakValueDictionary I didn't check for inconsistencies but was only annoyed but it's behavior. Guille and Denis: Instead of using SetElement or cleaning up the empty WeakValueAssociations, what I first thought is to internally consider an association with nil as absent. I mean, modify or override some methods soem when there is an WeakValueAssociation with value == nil it considers it's absent. Concretely, I'd expect: | dictionary | dictionary := WeakValueDictionary with: 'hello' -> 'world' copy. Smalltalk garbageCollect. { dictionary values includes: nil. *---> false * dictionary at: 'hello'. * ---> NotFound signal* dictionary at: 'hello' ifAbsent: [ 'absent' ].* ---> 'absent'* dictionary at: 'hello' ifAbsentPut: [ 'put' ]. *---> 'put'* } It's better if I give some context. Look this simplified version of my use case: MyUI>> morphAt: key cache ifNil: [ cache := WeakValueDictionary new ]. ^ cache at: key ifPresent: [:cachedValueOrNil | cachedValueOrNil ifNotNil: [ cachedValueOrNil ] ifNil: [ cache at: entryReference put: (self newMorph: key) ] ] ifAbsent: [ cache at: entryReference put: (self newMorph: key) ] I'd like to only send #newMorph: in ifAbsent: and to avoid the ifNotNil:ifNil: Like this: morphAt: key cache ifNil: [ cache := WeakValueDictionary new ]. ^ cache at: key ifAbsent: [ cache at: entryReference put: (self newMorph: key) ] :-) MartÃn