From: "Ara.T.Howard" <Ara.T.Howard@...>
Date: 2005-06-07T00:40:52+09:00
Subject: Re: How to call a class method when (i.e. in the moment of) inheriting from a class/defining a descendant?

On Mon, 6 Jun 2005, 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.

harp:~ > cat a.rb
class A
   class << self
     def setup
       puts "<#{ self }> invoking setup..."
     end
     def inherited klass
       klass.setup
     end
   end
end

class B < A
end

harp:~ > ruby a.rb
<B> invoking setup...

hth.

-a
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