From: "David A. Black" <dblack@...>
Date: 2005-11-27T09:36:42+09:00
Subject: Re: Nubish questions about syntax and gems

Hi --

On Sun, 27 Nov 2005, Ross Bamford wrote:

> On Sat, 26 Nov 2005 21:44:00 -0000, David A. Black <dblack@wobblini.net> 
> wrote:
>
>> What you've got basically is:
>>
>>   class A
>>     @@foo = "A's class variable foo"
>>   end
>>   @@foo = "Object's class variable foo"
>>   class B
>>     @@foo = "B's class variable foo"
>>   end
>> 
>> Since B is a subclass of Object, setting B's @@foo also sets Object's
>> @@foo.  The reason A's @@foo (when you see it via the instance eval)
>> does not change is that if you create a subclass's class variable
>> *first*, and then the superclass's (in this case, A and Object,
>> respectively), they are separate:
>> 
>> irb(main):002:0> class A; end; class B < A; @@foo = 1; end; class A;
>> @@foo = 2; puts @@foo; end
>> 2
>> => nil
>> irb(main):003:0> class B; puts @@foo; end
>> 1
>> David
>
> That's pretty subtle. Definitely one for the notebook.

Keep in mind too that class variable behavior is due to change in 2.0
(and I guess 1.9 too).  The new behavior is supposed to be more
strictly class-scoped, rather than hierarchy scoped.


David

-- 
David A. Black
dblack@wobblini.net