[Cuis-dev] Behavior of #superclass: message

[Juan Vuletich]

In addition to Martin's very good answer, I'll add a Cuis specific detail.

Regular classes are created by sending a message to the 
superclass-to-be. The problem is how to create subclasses of nil. In 
Cuis this is done in a rather hacky way:

ProtoObject subclass: #ProtoObject
     instanceVariableNames: ''
     classVariableNames: ''
     poolDictionaries: ''
     category: 'Kernel-Objects'.
ProtoObject superclass: nil

So first the class is created as subclass of something else and then the 
superclass is set to nil. However, ProtoObject class superclass is 
Class. And this trick shows in ClassDescription >> #definition. The 
reason for not simply sending 
#subclass:instanceVariableNames:classVariableNames:poolDictionaries:category: 
to nil (as it ised to be before we implemented this) is that a a missing 
class in a file-in would result in classes with unexpected nil 
superclass, instead of an error message.

I guess this all could be done in a clearer way. And this kind of hack 
is the only reason for #superclass:

HTH,

On 2025-11-27 5:42 PM, Facundo Javier Gelatti via Cuis-dev wrote:
> Hi!
>
> I've noticed that the #superclass: message does not affect the 
> superclass of the (meta)class of the receiver. For example:
>
> Object subclass: #A instanceVariableNames: '' classVariableNames: '' 
> poolDictionaries: ''.
> Object subclass: #B instanceVariableNames: '' classVariableNames: '' 
> poolDictionaries: ''.
>
> B superclass. " => Object "
> B class superclass. " => Object class "
>
> B superclass: A.
>
> B superclass. " => A "
> B class superclass. " => Object class (not A class)"
>
> The Class>>#superclass: method has a comment that says "Not to be used 
> lightly!", so I'm not sure if this is in fact the expected behavior 
> (but at least I was surprised by it).
>
> Cheers!
> Facu
>
-- 
Juan Vuletich
www.cuis.st
github.com/jvuletich
researchgate.net/profile/Juan-Vuletich
independent.academia.edu/JuanVuletich
patents.justia.com/inventor/juan-manuel-vuletich
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