From: Robert Klemme <bob.news@...>
Date: 2004-09-17T17:39:49+09:00
Subject: Re: class variable weirdness


"Bob Sidebotham" <bob@windsong.bc.ca> schrieb im Newsbeitrag
news:F7v2d.432470$M95.325276@pd7tw1no...
> This program runs, and prints "Foo" (as expected).
>
> module Mod
>    def get
>      @@var
>    end
>    @@var = "Mod"   # Removing this causes error
> end
>
> class Foo
>    include Mod
>    @@var = "Foo"
> end
>
> puts Foo.new.get
>
> -------------
>
> But if I remove the commented line, above, then I get:
>
>    uninitialized class variable @@var in Mod (NameError)
>
> This is with ruby 1.8.2 (2004-09-10) [i686-linux]
>
> Is this a bug, feature, or am I just missing something?

It's a speciality of class variables: they are visible in the class that
defines them and all sub classes.  So, if you remove the assignment in
Mod, it's defined in Foo and thus #get can't see it.  I know that sounds
wired but it's the way it is.  Personally I don't class variables and
that's why I try to avoid them if possible.

Kind regards

    robert