From: Stephen Bannasch <stephen.bannasch@...>
Date: 2006-04-11T08:55:52+09:00
Subject: Re: class variables and inheritance (ActiveRecord problem)

Here's a copy of my test case without using the ActiveSuppoprt's 
cattr_accessor method:

class Klass
   def prefix
     @@prefix
   end
   def prefix=(value)
     @@prefix=value
   end
   def Klass.show(string)
     puts @@prefix + string
   end
end

puts Klass.prefix.object_id

class DerivedKlass < Klass
   def prefix
     @@prefix
   end
   def prefix=(value)
     @@prefix=value
   end
end

puts DerivedKlass.prefix.object_id

Klass.prefix = "123"
Klass.show("abc") # => "123abc"
DerivedKlass.prefix = "789"
DerivedKlass.show("abc")# => "789abc"
Klass.show("abc") # => "789abc"

which produces:

2968188
2968188
123abc
789abc
789abc

I'd like to be able to create a class variable that will apply to all 
objects made from that class and ALSO create a derived class with a 
different class variable that is used in objects created from the 
derived class WITHOUT affecting the class variable defined in the 
original class.

It isn't obvious to me how to do this using class variables so either 
I'm missing something or there is another way to solve this 
programming problem. I'm going to look into how Ruby creates class 
variables.

-- 
- Stephen Bannasch
   Concord Consortium, http://www.concord.org