On Wed, Feb 22, 2017 at 12:57 AM, Martin Dias <tinchodias@gmail.com> wrote:
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.
Ah, ok, I only understood that you did not get why it was like that. :)
What I don't know is about using WeakRegistry
This is just needed to do the cleanup of the expired associations.
and Ephemerons.
This is a completely different thing. There is an EphemeronRegistry in the image, but it does not propose at:/at:ifAbsent: messages. It just holds Ephemerons. I'll check WeakKeyDictionary.
If you need to hold weakly the values, then this is not what you're looking for, isn't it?
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?
Yep. I would even call it: registerForCleanup Like that it is explicit that you're doing it, and that it may incur into some performance degradation of the entire system.
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:
Well, the idea of the SetElement is that you may want to have `nil` as a valid value in your dictionary. Otherwise, you cannot do: WeakValueDictionary new at: 'key' put: nil; at: 'key' --> error??? We can discuss if it is useful or not, but as with sets, before people used to check if the inserted element was nil beforehand to have the expected behavior...
| 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'* }
I agree that we may review the API. At least #at:, #at:ifAbsent: and #at:ifAbsentPut: should behave similarly. In any case, we could see how to improve EphemeronRegistry or even implement an EphemericDictionary that would replace the WeakValueDictionary.
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