2011/9/30 Nicolas Cellier <nicolas.cellier.aka.nice at gmail.com>:
> 2011/9/30 Bert Freudenberg <bert at freudenbergs.de>:
>>
>> On 29.09.2011, at 19:22, Rodney Polkinghorne wrote:
>>
>>> Dear list
>>>
>>> I wanted an array that lazily initialized elements 1 to n when you
>>> asked for the nth one.  So I ran something like:
>>>
>>> SequenceableCollection variableSubclass #Foo ...
>>>
>>> When I started a workspace, and tried Foo new: 10, my image hung.
>>>
>>> Eventually, I found the problem.  The workspace tried to print the
>>> answered instance, which resulted in it being sent a do: message to
>>> print its elements.  This ran the method
>>>
>>> SequenceableCollection>>do: aBlock
>>>       1 to: self size do:
>>>               [:index | aBlock value: (self at: index)]
>>>
>>> which ran
>>>
>>> Collection>>size
>>>       | tally |
>>>       tally := 0.
>>>       self do: [:each | tally := tally + 1].
>>>       ^ tally
>>>
>>> which sent do:, which sent size, which ...
>>>
>>> Is this considered a bug, or a learning experience for new players?
>>
>> The latter. You should not instantiate an abstract class. I don't think there is much that could be done about this.
>>
>> - Bert -
>>
>
> But Foo is a concrete class from Rodney, not Abstract.
> Generally, if the subclass must implement a method, it is expressed
> with an abstract implementation in the upper level
>    ^self subclassResponsibility
>
> Here, the subclass must implement a message, either #do: or #size but
> there is no explicit guidance.
> Personnally I consider this as very bad kernel code if not a bug.
> Does any subclass really use Collection>>size ?

OK, I just opened an image to check and only one does: LinkedList.
I suggest moving  Collection>>size implementation to LinkedList, and
replace it with a subclassResponsibility.

Nicolas

>
> Nicolas
>
>
>>> ArrayedCollection avoids it by restoring the primitive method for
>>> size.
>>>
>>> Rodney
>>>
>>
>>
>>
>>
>