From: Timothy Hunter <TimHunter@...>
Date: 2007-03-25T10:52:45+09:00
Subject: Re: class methods and instance variables in ActiveRecord::Base

zig wrote:
> On Mar 24, 3:56 pm, "Giles Bowkett" <gil...@gmail.com> wrote:
>
>   
>> The answer to your question is that the class which inherits is opened
>> up, and this method is defined within it. Not the instances -- the
>> instances are untouched. This opens up the Class object itself. Then,
>> obviously, it sets an instance variable. At that point, what it's
>> doing is setting an instance variable of the Class object.
>>
>>     
>
> OK, I think I'm getting there.
>
> Is an instance variable of the class object the same thing as a class
> variable?
>
> For example, consider
>
> class A
>  @@var1
> end
>
> and
>
> class A
>  class << self
>   attr_reader :var1
>   attr_writer :var1
>  end
> end
>
> In both cases I call that variable with A.var1.  Are they the same?
>
>
>   
A class variable is NOT the same as an instance variable of the class 
object. Have you tried "calling" @@var1 with A.var1? It doesn't work. 
The attr_reader and attr_writer methods create methods that operate on 
@var1. There is no method "var1" that operates on @@var1.