From: Kyle Rawlins <rawlins@...>
Date: 2002-06-14T02:49:26+09:00
Subject: Re: The need for metaclasses (was Re: Ruby for jMax)


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On Fri, Jun 14, 2002 at 01:19:47AM +0900, Ned Konz wrote:
> After all, classes are not essential for object-oriented programming.=20

Well, I certainly agree with that.  However, it seems to me that if you're
using a language which does have classes, especially one where everything i=
s an
object, the most consistent way to abstract what a class is is have some ob=
ject
that represents a class.  Consistency would then further cause you to have =
some
class that describes that object.  There are other ways to do it in languag=
es
which have classes, but to me it's a matter of consistency.  But perhaps I
should stop here since I'm not really experienced enough to judge one way or
the other about metaclasses in the long run, I just think they're neat.

> Though they've been a comfortable concept in many languages, all you=20
> really need for OO is objects. Inheritance, classes as objects, etc.=20
> aren't required.

I actually think quite a few people would disagree with this statement.  The
thing that has differentiated what has been called object oriented programm=
ing
from simple data abstraction/ADTs (which has been used in non-OO languages =
for
ages) is having some kind of relationship between the objects.  If you simp=
ly
take the name 'object oriented programming' and analyse it, yes, it seems t=
hat
all you need are objects.  But the things that have been called OO at least
that I know of, have all gone beyond data abstraction to have relationships.
This doesn't necessarily have to be expressed as classes and inheritance, b=
ut
the common thread does seem to be some approximation of the subtype relatio=
n.
Also, to me, the presence of these relationships is one of the things which
makes the languages interesting.

-kyle

--=20
http://mas.cs.umass.edu/~rawlins
--
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