[Cuis-dev] nil subclasses (Re: clever or silly idea?)

[Juan Vuletich]

On 6/12/2024 1:06 PM, Andres Valloud via Cuis-dev wrote:
> Hi,
>
>> 3. This is another issue. If you see the definition of ProtoObject in
>> the browser, or the comment at UndefinedObject >> 
>> #subclass:instanceVariableNames:classVariableNames:poolDictionaries:category:
>> , the recommended way to create the class is to make it subclass of
>> Undefined object, and then do `Parrot superclass: nil`. This is
>> disturbing.
>
> Agreed.
>
>> Parrot will have superclass == nil, but will be included
>> in the subclasses array of ProtoObject. The superclass / subclass
>> invariant is broken. This code has been there for 25 years, and I
>> wouldn't modify it lightly. Moreover, if you evaluate the suggested
>> class definition, it will appear repeated times, like ProtoObject
>> subclasses = #(Object MessageCatcher BreakingMethodWrapper Parrot
>> Parrot Parrot Parrot) . So something has to be done.
>
> Oof, what a mess.  Strange, I do not remember this behavior from 
> Squeak back in the early 2000s, and I am sure I was creating 
> subclasses of nil at the time.  Maybe it's been too long.

Just pushed a fix for this.

>
>> I guess the only subclass of nil created in 25 years is ProtoObject 
>> itself...
> Well, if you get silly behavior like what you describe, that sure acts 
> as a disincentive :).
>
> Andres.


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Juan Vuletich
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