From: David Alan Black <dblack@...>
Date: 2002-02-12T05:22:23+09:00
Subject: Re: Class variable madness

Hello --

On Tue, 12 Feb 2002, Joel VanderWerf wrote:

> Yukihiro Matsumoto wrote:
> ...
> > That's what class variables are.  Class variables are variables to be
> > shared among class hierarchy.  They are not only shared by instance of
> > the class, but also shared by instances of subclasses.  As a result,
> > you cannot define class variables of same names in subclass.
> >
> >                                                         matz.
>
> ...unless you define it in the subclass *first*, right?
>
> irb(main):001:0> class A; end
> nil
> irb(main):002:0> class B<A; @@x=0; end
> 0
> irb(main):003:0> class A; @@x=1; end
> 1
> irb(main):004:0> class B; @@x; end
> 0
> irb(main):005:0> class A; @@x; end
> 1
>
> So the semantics depends on the order of definition. Because of this
> behavior, I treat class vars sort of like globals and use them only in
> prototype code, quick and dirty code, etc. For code that I can think
> about more (and expend more keystrokes), I use class instance variables,
> and write a bunch of accessors.

This came up in some discussion about class variables last year.  Matz
said in [ruby-talk:19974]:

   I know this happens.  I consider this as an error that Ruby does not
   detect yet.


David

-- 
David Alan Black
home: dblack@candle.superlink.net
work: blackdav@shu.edu
Web:  http://pirate.shu.edu/~blackdav