1.1 -- Inconsistent enumeration behavior of WeakKeyDictionary and subclasses

> If you run this in 1.1:
>
> | dict |
> dict := WeakKeyDictionary new.
> dict at: 'foo' copy put: 'bar'.
> Smalltalk garbageCollect.
> dict associationsDo: [:assoc | self halt].
> dict do: [:val | self halt]
>
>
> It stops in the second halt, but not the first.
>
> This is because #associationsDo: does not include associations whose
> keys have been GCed, but #do: *does* include values whose corresponding
> keys have been GCed.
>
> This behavior seems inconsistent, and not particularly useful, and also
> seems to contradict the comments by the author in the Squeak bug from
> 2007, from which I'd think that #do: would not include the value which
> it currently does.
>

>
> Comments?
>
> Regards,
>
> -Martin
>
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> [hidden email]
> http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project
>

> 2009/12/31 Martin McClure <[hidden email]>:
>> If you run this in 1.1:
>>
>> | dict |
>> dict := WeakKeyDictionary new.
>> dict at: 'foo' copy put: 'bar'.
>> Smalltalk garbageCollect.
>> dict associationsDo: [:assoc | self halt].
>> dict do: [:val | self halt]
>>
>>
>> It stops in the second halt, but not the first.
>>
>> This is because #associationsDo: does not include associations whose
>> keys have been GCed, but #do: *does* include values whose corresponding
>> keys have been GCed.
>>
>> This behavior seems inconsistent, and not particularly useful, and also
>> seems to contradict the comments by the author in the Squeak bug from
>> 2007, from which I'd think that #do: would not include the value which
>> it currently does.
>>
> It is useful in terms, that sometimes you don't want to see the
> objects which GCed,
> but sometimes do. See how WeakRegistry using this.
> The lack of ephemerons support in VM, forcing us to deal with such
> things manually.

>
>> So I *think* this is an oversight, and is easy to fix by defining
>> WeakKeyDictionary>>do: in terms of self associationsDo:.
>>
>> But then there's the question of #size. The collection above answers 1
>> to #size, which also seems wrong.
>>
> #size for weak key dict is non-deterministic. Because even if you want to know
> the exact number of elements, you will need to iterate over the
> collection, but then,
> iteration can trigger GC, and you have a big chances to answer wrong value.

> Igor Stasenko wrote:
>> 2009/12/31 Martin McClure <[hidden email]>:
>>> If you run this in 1.1:
>>>
>>> | dict |
>>> dict := WeakKeyDictionary new.
>>> dict at: 'foo' copy put: 'bar'.
>>> Smalltalk garbageCollect.
>>> dict associationsDo: [:assoc | self halt].
>>> dict do: [:val | self halt]
>>>
>>>
>>> It stops in the second halt, but not the first.
>>>
>>> This is because #associationsDo: does not include associations whose
>>> keys have been GCed, but #do: *does* include values whose corresponding
>>> keys have been GCed.
>>>
>>> This behavior seems inconsistent, and not particularly useful, and also
>>> seems to contradict the comments by the author in the Squeak bug from
>>> 2007, from which I'd think that #do: would not include the value which
>>> it currently does.
>>>
>> It is useful in terms, that sometimes you don't want to see the
>> objects which GCed,
>> but sometimes do. See how WeakRegistry using this.
>> The lack of ephemerons support in VM, forcing us to deal with such
>> things manually.
>
> I see the value in being able to choose both. WeakRegistry uses
> #allAssociationsDo:, not #associationsDo:. Seems like it would be more
> consistent to also have an #allDo: that includes values of collected
> keys, and a #do: that does not.
>

>>
>>> So I *think* this is an oversight, and is easy to fix by defining
>>> WeakKeyDictionary>>do: in terms of self associationsDo:.
>>>
>>> But then there's the question of #size. The collection above answers 1
>>> to #size, which also seems wrong.
>>>
>> #size for weak key dict is non-deterministic. Because even if you want to know
>> the exact number of elements, you will need to iterate over the
>> collection, but then,
>> iteration can trigger GC, and you have a big chances to answer wrong value.
>
> That seems reasonable, though there's no effort to even come close in size.
>

>
>>
>>> So I *think* this is an oversight, and is easy to fix by defining
>>> WeakKeyDictionary>>do: in terms of self associationsDo:.
>>>
>>> But then there's the question of #size. The collection above answers 1
>>> to #size, which also seems wrong.
>>>
>> #size for weak key dict is non-deterministic. Because even if you want to know
>> the exact number of elements, you will need to iterate over the
>> collection, but then,
>> iteration can trigger GC, and you have a big chances to answer wrong value.
>
> That seems reasonable, though there's no effort to even come close in size.
>
> -Martin
>
> _______________________________________________
> Pharo-project mailing list
> [hidden email]
> http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project