On Tue, Feb 21, 2017 at 10:37 AM, Denis Kudriashov <dionisi...@gmail.com>
wrote:
> Hi.
>
> 2017-02-21 9:44 GMT+01:00 Guillermo Polito <guillermopol...@gmail.com>:
>
>> Hi Dr. Dias,
>>
>> a WeakValueDictionary get's its values collected if they are not
>> referenced strongly. However, the association remains there. This means
>> that when you do:
>>
>> dictionary := WeakValueDictionary with: 'hello' -> nil copy.
>>
>> You'll have something like this:
>>
>> WeakValueDictionary {
>> WeakValueAssociation { key: 'hello', value: yourObject }
>> }
>>
>> Once you garbage collect, the value is holding yourObject weakly, so
>> you'll have:
>>
>> WeakValueDictionary {
>> WeakValueAssociation { key: 'hello', value: nil }
>> }
>>
>> But the WeakValueAssociation will still be there.
>>
>>
> For me what you describe is implementation details and users should not
> think about it at all.
>
Of course it is an implementation detail. I'm just describing how it works
(and thus, how it does not work).
I never said it was a good or bad approach.
I agree ifAbsent~ messages should work with collected values by "absent
> branch". It is intuitive.
>
> To support it correctly we can use approach of Set which uses
> #asSetElement to store items. Then we can easily distinguish nil from
> absent value. Real nil value will happen only by garbage collection.
> But I am wondering WeakSet not uses SetElement approach directly and
> instead it uses special flag object. Maybe it should be fixed too.
>
But in any case, whatever the alternative you give users, they must
understand the tradeoff. If all Weak*Dictionaries were subscribed by
default to the weak registry for cleanup, that would provoke a lot of
overhead during garbage collection.
Magic is good in some cases, but when you're dealing with low level stuff
explicitly (like instantiating a Weak*Dictionary) I prefer to control some
of that magic explicitly.
