From: Christoph <chr_mail@...>
Date: 2005-04-25T01:03:54+09:00
Subject: Re: [ANN] Article: Seeing Metaclasses Clearly

gabriele renzi schrieb:

>>
>
> I disagree, thinking that mixins and multiple inheritance are not the 
> same thing, and should not be pointed as such.

I tend to agree with Mathieu that the semantically insistence that 
Ruby's mixins
are NOT some kind of MI of presents itself as a language game to
apiece the java kraut. On the other hand Ruby�s "Module mixin" relation is
NOT transitive, making it strikingly different from (single or multiple)
inheritance (see for example [ruby-talk:32007])



>
>> The defining qualities of a Ruby class may be that:
>>
>> 1. a Ruby class is a direct-subclass-of a Ruby class using the "<" 
>> notation (except the Object class).
>>
>> 2. the Object class just happens to be the place where .new() is 
>> defined; and this is no matter how many classes use 
>> undef_method(:new) to forbid instantiation.
>
>
> Is'nt it Class#new ?

Mathieu might be nominally wrong, but he is right in pointing out that 
the current distinction between
"meta Object" (the singleton class of the "Class" object "Object") and 
the class "Class" is just an artifact
of the current implementation of Ruby�s Object model. Two or three years 
ago I even cooked up a
semi working modification of the interpreter (translation: the resulting 
interpreter finished without crashing
running a couple of simple scripts), such that "meta Object" == Class 
was true.

The strongest argument against "meta Object" == Class are the current 
class relations
Class < Module < Oject.
To resolve this we could subclass both Module and Class from Object 
directly, or settle on relations
Module < Class < Object

Another possibility, would be getting rid of the class Module 
altogether, by either relying on full-blown MI
or restricting the mixins to special "Module classes". Any of these 
alternative schemes have their shortcomings,
but the current Class < Module < Object isn't flawless either.


/Christoph