From: ara.t.howard@...
Date: 2007-01-25T00:48:56+09:00
Subject: Re: Trickery in the ancestors chain

On Wed, 24 Jan 2007, Paolo Nusco Perrotta wrote:

> Try this:
>
>  module M
>    def hello; p 'M'; end
>  end
>
>  class C
>    def hello; p 'C'; end
>  end
>
>  class D < C; end
>
>  class C; include M; end
>  class D; include M; end
>  D.ancestors                      -> [D, C, M, Object, Kernel]
>  D.new.hello                       -> "C"
>
>
> Now restart from a clean slate and change the last few lines:
>
>  class D; include M; end
>  class C; include M; end
>  D.ancestors                      -> [D, M, C, M, Object, Kernel]
>  D.new.hello                       -> "M"
>

>
> Ruby silently prevents you from including a module that has been
> included by an ancestor. Why?
>

why do you say that?  you first tell D to include M, which ruby does.  then
you tell C to include M, which ruby does.  that's why M is in the ancestors
list twice.  am i missing something.  try working with this from the console
so we're on the same page:

   harp:~ > cat a.rb
   #
   # take one
   #
     module M
       def hello; 'M'; end
     end
     class C
       def hello; 'C'; end
     end
     class D < C; end
     class C; include M; end
     class D; include M; end
     p D.ancestors                      #=> [D, C, M, Object, Kernel]
     p D.new.hello                      #=> "C"
   #
   # take two
   #
     Object.instance_eval{
       remove_const 'C'
       remove_const 'D'
     }
     class C
       def hello; 'C'; end
     end
     class D < C; end
     class D; include M; end
     p D.ancestors                      #=> [D, M, C, Object, Kernel]
     class C; include M; end
     p D.ancestors                      #=> [D, M, C, M, Object, Kernel]
     p D.new.hello                      #=> "M"


   harp:~ > ruby a.rb
   [D, C, M, Object, Kernel]
   "C"
   [D, M, C, Object, Kernel]
   [D, M, C, M, Object, Kernel]
   "M"

this makes perfect sense to me attm - you're picking up 'hello' from M and it's
first up the method lookup chain.  but maybe i'm not understanding?

regards.

-a
-- 
we can deny everything, except that we have the possibility of being better.
simply reflect on that.
- the dalai lama