From: Bill Kelly <billk@...>
Date: 2002-12-02T11:52:07+09:00
Subject: Re: class << self  (was Re: [FAQ] What do some of Ruby's symbols mean?)

Hi Gavin,

From: "Gavin Sinclair" <gsinclair@soyabean.com.au>


> > class Array
> >   def instancemethod
> >     [define]
> >   end
> >
> >   class << self
> >     def classmethod
> >       [define]
> >     end
> >   end
> > end
> >
> > There's no arcane magic going on here - self is an object of class
> > Class, and in this case it has the value Array.
> 
> That, to me, is obfuscated.  'self' is generally understood as the current
> instance of the class.

Yes!

>  Therefore, it is only meaningful inside instance methods.

Hang on.... let the beauty of Ruby flow through you....  (Heh,
sorry - I was considering attempting some corny Star Wars reference,
culminating in, 'You've taken your first step into a larger world...'
.... but I've out-cornballed myself, and I can't go through with it ;)

The beauty here, folding in meta-classes into the mix - and, as I
understand it - is: Class, and the definitions thereof, in Ruby, are
less of a special case than languages such as C++ or Java.  'self' *is*
relevant inside a class definition in Ruby.  Think about the possible
implications of the interpreter actually executing statements inside
a class definition when they occur in the source...

irb> class X
irb>   @@my_self = self  # consider executed right now during the definition of 'X'
irb>   def X.my_self; @@my_self; end
irb> end
nil
irb> X.my_self
X
irb> X.my_self.class
Class
irb> X.my_self.methods.include? "my_self"
true
irb> X.id
22405636
irb> X.my_self.id
22405636

'self' during the definition of class X, is an *instance* of Class.
It's the particular instance of Class representing X.

. . . Anyway, I'd recommened the section in chapter 19 of Pickaxe,
entitled, "What's the Meta?" -- I just re-read it myself and I'd
forgotten a bit of it............

Uhhhhhh... hope this helps <grin>

Regards,

Bill