From: Gennady Bystritksy <gfb@...>
Date: 2005-06-07T00:38:19+09:00
Subject: Re: How to call a class method when (i.e. in the moment of) inheriting from a class/defining a descendant?

You must keep in mind that a class instance variable is local for the 
particular class object. In your case, trying to set @x in B does it 
locally for class B, not affecting @x in class A in any way, even when B 
inherits from A. You may want to define "attr_writer :x" in class A and 
use "self.x = 'something'" in class B.

Gennady.

Thomas wrote:
> Hi,
> 
> This problem maybe results from a bad understanding of what I'm trying 
> to do. Anyway, is it possible to call a method when creating a new class 
> or inheriting from another class?
> 
> Currently my code looks somehow like this:
> 
> class A
>     class << self
>         attr_reader :x
> 
>         def prepare
>             # do something
>         end
> 
>         def fixate
>             # do something
>         end
> 
>         def foo(a)
>             # do something with a and @x
>         end
>     end
> end
> 
> class B < A
>     prepare
> 
>     @x = "something"
> 
>     foo("bar")
> 
>     def method1
>         # do something else
>     end
> 
>     fixate
> end
> 
> Now in an ideal world, the definition of class B would be simply:
> 
> class B < A
>     @x = "something"
> 
>     def method1
>         # do something
>     end
> end
> 
> and A.setup and A.fixate should be automagically invoked whenever 
> defining a descendant from class A.
> 
> Does somebody know a solution for how this can be done? The only 
> possible way of doing this I could come up with is to wrap the 
> definition part into a block and pass this block to a method that calls 
> these functions and evaluates the block using class_eval. Something in 
> the line of (untested):
> 
> class C < A
>     wrapper do
>         @x = "something"
> 
>         def method1
>             # do something
>         end
>     end
> end
> 
> But I'm not sure if this solution really is an advantage.
> 
> Cheers,
> Thomas.
> 
>