From: Patrick Bennett <patrick.bennett@...>
Date: 2003-08-22T13:59:54+09:00
Subject: Re: Class variables - a surprising result

Dan Doel wrote:

>
> @variables are only like C++ instance variables when used within 
> instance methods.  If you do:
>
> class Foo
>    @var = 6
>      def Foo.print
>       p @var
>    end
>
>    def print
>       p @var
>    end
> end
>
> Then:
>
> Foo.print # => 6
> Foo.new.print # => nil 

Geesh - sneaky stuff..  This kind of thing *definitely* violates the 
P.O.L.S. imo.  For one, having the 'same' variable actually be two 
different 'instances' (one, a class variable effectively,
and another, an instance variable) is very confusing.  I understand it 
now (although I have to think about it for a sec, and personally, I 
think that's a bad sign).
I think the above @var=6 assignment outside of a method decl should be 
illegal.  It should have to be a @@ reference.

> If you want to access these in instance methods, you need to do:
>
> class Foo
>    def instance_meth
>       p self.class.class_eval { @var }
>    end
> end 

Cool - and interesting, but if I ever saw this in somebody's code, 
well....  let's just say I'd give them a stern look.  ;)

> ...
>
> So it is effectively a class instance variable, although that's still 
> not the same as a Java static
> variable, since it's not inherited. 

Still not the same. ;)