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. :)

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What I don't know is about using��WeakRegistry

This is just needed to do the cleanup of the expired associations.

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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.��

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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) ]

:-)

Mart��n