From: Sean O'Halpin <sean.ohalpin@...>
Date: 2005-11-11T09:18:27+09:00
Subject: Re: A question about class variable

On 11/10/05, Sam Kong <sam.s.kong@gmail.com> wrote:
> Hello!
>
> I have a question about class variable.
>
> class C1
>  @@a = "C1"
>  def f
>    @@a
>  end
> end
>
> class C2 < C1
>  @@a = "C2"
> end
>
> puts C2.new.f   #=> "C2"
If you add the line:

  puts C1.new.f   #=> "C2"

you'll see that the @@a you set in C2 is actually the same @@a as
defined in C1. Class variables in Ruby 1.8.2 are a more like 'class globals'.
All subclasses share the same variable.

> I assume that the method f should behave polymorphically and the body
> of f should be interpreted in the context of C2's instance method if I
> call it via an instance of C2.

Ah assumptions! ;) The body of f ~is~ interpreted in the context of
C2's instance, but the @@a is scoped to the class in which f is
~defined~.

HTH

Regards,

Sean