From: dblack@...
Date: 2006-06-24T06:49:25+09:00
Subject: Re: class << self?

Hi --

On Sat, 24 Jun 2006, Erik Veenstra wrote:

> On Sat, 2006-06-24 at 05:36 +0900, Roger Johansson wrote:
>
>> thanks, Ive figured this part out.
>>
>> but what exactly does the class << self do? why do I need it,
>> why cant I just do "alias bla,orig" on static methods
>> directly?
>
> Data is stored in objects. Code is stored in classes. You can't
> store data in classes and you can't store code in objects. It's
> just that simple.

Classes are objects, though (as you point out later in a slightly
different context), so they can store data:

   class C
     @x = 1
   end

> But...
>
> Let's have a look at this code:
>
> foo = Foo.new
> def foo.bar
>   # code...
> end
> foo.bar
>
> This adds method bar to foo. Not to Foo, but to "that specific
> instance of Foo". Uh, that doesn't match very well with my
> first statement about class and objects, does it?
>
> So Matz gave us meta classes, or anonymous classes, or, virtual
> classes. Different names for the same thing.

Namely, singleton classes :-)  (I know, I know.)

> Every Object can have a classes of its own where it can store code.
> That's the trick.

Those terms aren't interchangeable, though; a class can be anonymous
without being the singleton class of an object:

   Class.new

Singleton classes are anonymous, but anonymous classes aren't always
singleton classes.


David

-- 
David A. Black (dblack@wobblini.net)
Ruby Power and Light, LLC (http://www.rubypowerandlight.com)

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