From: "David A. Black" <dblack@...>
Date: 2005-10-03T21:26:17+09:00
Subject: Re: Cannot subclass Class?

Hi --

On Mon, 3 Oct 2005, Hal Fulton wrote:

> David A. Black wrote:
>> 
>> Singleton classes in general are definitely not deep magic.  They're
>> just the way Ruby handles requests for per-object method definitions:
>> stick them in a per-object class.  They're not particularly meta;
>> they're just anonymous classes.
>
> It has always bothered me a tiny bit to call them classes at all;
> after all, you can't instantiate them. What kind of class has no
> instances? The Unicorn class perhaps?

Well, the major example that comes to mind is the singleton class in
Ruby :-)  But I understand the misgivings.  Matz has talked about
making them some other kind of "class-like object" in the future.  I'm
not rooting for that, though.  The reason I like having them be
classes is the great simplicity of the whole design: you just insert
the singleton class on the method search path, and it fits in so
nicely.  No need to explain (and I always find myself thinking in
terms of explaining these things) a completely different entity for
this one case.

I suppose one could also say that it's the ultimate emblem of the
class-based/prototype-based hybrid nature of Ruby: a class that
expresses the liberation of the object from its class ancestry.


David

-- 
David A. Black
dblack@wobblini.net