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

[Andres Valloud]

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.

> 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.