From: Brian Candler <B.Candler@...>
Date: 2003-08-06T16:10:56+09:00
Subject: Re: Class variables, module inclusion and instance_eval

On Wed, Aug 06, 2003 at 02:55:31PM +0900, Tim Bates wrote:
> Somehow, even though the class variable is defined within the context of
> the class (via instance_eval) it still gets shared, contrary to the
> example of Exhibit B. This is frustrating me, because I want my library
> to be able to define a class variable that belongs to only one class,
> and I can't find a way to do it.

I can't answer your clearly-phrased questions on class variables, but there
might be another solution: class instance variables. They are private to the
class, not even inherited by subclasses. They're not particularly convenient
to use though, because within an instance method, '@foo' refers to the
instance variable of the instance of A, not of the class of A.

But they do work:

module Foo
  def self.append_features(aModule)
    super
    aModule.instance_eval { @foo = Time.now }
  end
  def foo
    self.class.instance_eval { @foo }
  end
end

class A
include Foo
end

p A.new.foo

sleep 2

class B
include Foo
end
p B.new.foo

p A.new.foo

Regards,

Brian.