From: ara.t.howard@...
Date: 2006-10-17T23:25:31+09:00
Subject: Re: metaprogramming surprise?

On Tue, 17 Oct 2006, Artur Merke wrote:

> OK, but why are they not the same???

because the solve different problems:

     harp:~ > cat a.rb
     class A
       @@class_var = "one for all descendants"
       @class_instance_var = "one per class"

       class << self
         attr_accessor "class_instance_var"

         def class_var() @@class_var end
         def class_var=(val) @@class_var = val end
       end

       attr_accessor "instance_var"

       def initialize s
         @instance_var = "one per instance (#{ s })"
       end
     end

     class B < A
     end


     a = A.new 'a'
     b = B.new 'b'

     require "yaml"

     puts "---"
     y "a.instance_var"       => a.instance_var
     y "b.instance_var"       => b.instance_var
     y "A.class_var"          => A.class_var
     y "B.class_var"          => B.class_var
     y "A.class_instance_var" => A.class_instance_var
     y "B.class_instance_var" => B.class_instance_var

     B.class_instance_var = "this one is just for B"

     puts "---"
     y "a.instance_var"       => a.instance_var
     y "b.instance_var"       => b.instance_var
     y "A.class_var"          => A.class_var
     y "B.class_var"          => B.class_var
     y "A.class_instance_var" => A.class_instance_var
     y "B.class_instance_var" => B.class_instance_var


     harp:~ > ruby a.rb
     ---
     a.instance_var: one per instance (a)
     b.instance_var: one per instance (b)
     A.class_var: one for all descendants
     B.class_var: one for all descendants
     A.class_instance_var: one per class
     B.class_instance_var:
     ---
     a.instance_var: one per instance (a)
     b.instance_var: one per instance (b)
     A.class_var: one for all descendants
     B.class_var: one for all descendants
     A.class_instance_var: one per class
     B.class_instance_var: this one is just for B


regards

-a
-- 
my religion is very simple.  my religion is kindness. -- the dalai lama