What is a "weak" reference

> Bert Freudenberg a écrit :
>> Am 15.07.2008 um 08:26 schrieb Herbert König:
>>> Hello Randal,
>>>
>>> RLS> dictionary.  This is how the classic "dependents" system  
>>> works as well: the
>>> RLS> dependencies are in a WeakDictionary so that when the watched  
>>> object goes
>>> RLS> away, the dependencies are also cleaned.
>>>
>>> thanks for some free education (no smiley, I mean it), now I'll do
>>> some homework and look up dependency.
>>>
>>> I use it in some places without knowing of it's "weakness".
>> The dependents are weak only for "regular" objects. Proper Models  
>> handle their own dependents collection in a non-weak manner.
>> - Bert -
>
> Hmm, not really
>
> "Warning: this example is stupid!"
> | tmp |
> tmp := Model new.
> tmp addDependent: #x.
> tmp addDependent: #y.
> tmp dependents class. "=> DependentsArray"
>
> DependentsArray is a class that holds weakly to its elements...
>
> The difference is that the DependentsArray itself don't have to  
> pollute the global WeakIdentityKeyDictionary (Object classPool at:  
> #DependentsFields).

>
> Am 15.07.2008 um 13:23 schrieb nicolas cellier:
>
>> Bert Freudenberg a écrit :
>>> The dependents are weak only for "regular" objects. Proper Models
>>> handle their own dependents collection in a non-weak manner.
>>> - Bert -
>>
>> Hmm, not really
>>
>> "Warning: this example is stupid!"
>> | tmp |
>> tmp := Model new.
>> tmp addDependent: #x.
>> tmp addDependent: #y.
>> tmp dependents class. "=> DependentsArray"
>>
>> DependentsArray is a class that holds weakly to its elements...
>>
>> The difference is that the DependentsArray itself don't have to
>> pollute the global WeakIdentityKeyDictionary (Object classPool at:
>> #DependentsFields).
>
> You are right, I was mislead by Object>>dependents ...
>
>> But maybe we have just quit the beginners rails...
>
>
> ... and you are right again.
>
> - Bert -

> While we are at it, here is a lesson i learned recently:
>
>      | weak obj |
>      weak := WeakIdentityKeyDictionary new.
> "Create an Object"
>      obj := Object new.
> "Add a weak reference to this Object"
>      weak at: obj put: (Array with: obj).
> "This DoIt methods points to the Object via it's temporary variable.
> Clear this pointer, so that the Object can eventually be reclaimed"
>      obj := nil.
> "Now garbageCollect to reclaim the weak references"
>      Smalltalk garbageCollect.
> "Let us see if the Object was reclaimed:"
>      ^weak size
>
> Why the object obj was not reclaimed?