From: "Mauricio Fernández" <batsman.geo@...>
Date: 2003-06-19T15:20:34+09:00
Subject: Re: Class variables in parent and child classes with the same name

On Thu, Jun 19, 2003 at 09:17:48AM +0900, Zellyn Hunter wrote:
> Am I misunderstanding something, or can you not give a child class a class 
> variable with the same name as a parent class?  Just curious.

Right, class variables are "tree scoped", meaning that they're accessible
downwards from the point in the class hierarchy they were first
assigned:

batsman@tux-chan:/tmp$ expand -t2 /tmp/ax.rb

class A
  def foo= o
    @@foo = o
  end
  def foo
    @@foo
  end
end

class B < A
  def bar= o
    @@foo = o
  end
  def bar
    @@foo
  end
end

a = B.new
a.bar = 'bar'
puts a.bar
a.foo = 'foo'
puts a.foo
puts a.bar
a.bar = 'bar'
puts a.foo

batsman@tux-chan:/tmp$ ruby /tmp/ax.rb
bar
foo
/tmp/ax.rb:16: warning: class variable @@foo of A is overridden by B
bar
/tmp/ax.rb:13: warning: class variable @@foo of A is overridden by B
foo

> It seems to work as one would expect for constants, but obviously one couldn't 
> use a constant to keep track of information.

You can get the desired behavior with class instance variables:

batsman@tux-chan:/tmp$ expand -t2 /tmp/aw.rb
class Parent
  @count = 1
  class << self; attr_reader :count end

  def parentCount
    Parent.count
  end
end

class Child < Parent
  @count = 2

  def childCount
    Child.count
  end
end

p = Parent.new
c = Child.new
puts p.parentCount
puts c.childCount
puts c.parentCount
batsman@tux-chan:/tmp$ ruby /tmp/aw.rb
1
2
1

-- 
 _           _                             
| |__   __ _| |_ ___ _ __ ___   __ _ _ __  
| '_ \ / _` | __/ __| '_ ` _ \ / _` | '_ \ 
| |_) | (_| | |_\__ \ | | | | | (_| | | | |
|_.__/ \__,_|\__|___/_| |_| |_|\__,_|_| |_|
	Running Debian GNU/Linux Sid (unstable)
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