From: "David A. Black" <dblack@...>
Date: 2004-02-14T11:09:04+09:00
Subject: Re: accessing constants from class methods

Hi --

On Sat, 14 Feb 2004, Ara.T.Howard wrote:

> 
> what i would like to accomplish would be something like this:
> 
> 
>   class Abstract 
>     class << self
>       def x
>         # defined?(self::X)  ? self::X : nil
>       end
>     end
>   end
> 
>   class Concrete < Abstract 
>     X = 42
>   end
> 
>   # p Base.x    # => nil
>   # p Derived.x # => 42

        ^^^^^^^  you mean Abstract/Concrete, I assume :-)


I think this already does what you want, doesn't it?

  $ cat ara.rb
     class Abstract
       class << self
	 def x
	    defined?(self::X)  ? self::X : nil
	 end
       end
     end

     class Concrete < Abstract
       X = 42
     end

     p Abstract.x
     p Concrete.x

  dblack@laptop:~/hacking$ ruby -v ara.rb
  ruby 1.6.8 (2002-12-24) [i686-linux-gnu]
  nil
  42

on the general principle that self will get set to the
receiver (Concrete, in this case) -- so, for example:

  irb(main):001:0> class A; def A.x; p self; end; end
  => nil
  irb(main):002:0> class B < A; end
  => nil
  irb(main):003:0> B.x
  B

(Or did I misunderstand?)


David

-- 
David A. Black
dblack@wobblini.net