From: Mathieu Bouchard <matju@...>
Date: 2005-04-24T23:35:57+09:00
Subject: Re: [ANN] Article: Seeing Metaclasses Clearly

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On Sun, 24 Apr 2005, gabriele renzi wrote:
> Mathieu Bouchard ha scritto:
>> On Thu, 21 Apr 2005, ts wrote:
>>> * a class is a module which can use inheritance
> I disagree, thinking that mixins and multiple inheritance are not the sam=
e=20
> thing, and should not be pointed as such.

Take a look at the inheritance mechanism in CommonLISP and how the=20
(call-next-method) macro works in LISP and then you won't be able to=20
honestly tell me that mixins are not inheritance and that Ruby's mixins=20
aren't like Lisp's classes. Really. Go see for yourself.

>> 1. a Ruby class is a direct-subclass-of a Ruby class using the "<" notat=
ion=20
>> (except the Object class).
>> 2. the Object class just happens to be the place where .new() is defined=
;=20
>> and this is no matter how many classes use undef_method(:new) to forbid=
=20
>> instantiation.
> Is'nt it Class#new ?

Sorry, yes. But it amounts to the same thing, because the (Object)=20
metaclass is the sole direct descendant of Class, and the creation of a=20
new class never can add a new direct descendent to Class, and so it would=
=20
be possible to unify the (Object) metaclass and the Class class and=20
frankly no-one would notice.

Guy Decoux and you are right on this detail, but this detail is not=20
important in my point, and here is what I mean: I mean that what makes a=20
class a class is that it inherits from whatever is the sole authority for=
=20
making new objects, and that's something that non-class modules don't have=
=20
access to.

(And although there *are* some pieces of code that might construct new=20
objects without the help of Class#new, it isn't the one you can use for=20
building objects of your own custom-designed non-singleton classes)

Does that clear up things a bit?

  ,-o---------o---------o---------o-. ,----.                            |
  | The Diagram is the Program (TM) | |  ,-o----------------------------o-.
  `-o-----------------------------o-' |  | Mathieu Bouchard (Montr=E9al QC)=
 |
    |                             |---'  |      http://artengine.ca/matju |
    |                             |      `-o------------------------------'

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