From: ara.t.howard@...
Date: 2006-05-04T11:55:28+09:00
Subject: Re: mixin puzzle

On Thu, 4 May 2006, Mike Harris wrote:

> I had no idea that extend has an append_features-style callback, you
> learn something every day.  Thanks Mauricio.

i think you should elaborate on what you really want, what mauricio posted,
though cool, definitely modifies the class:

   harp:~ > cat a.rb
   module N
     class << self; attr_accessor :bleh end # just to prove #foo was run
     self.bleh = "#foo not executed"
     def foo
       N.bleh = "#foo was executed!!"
     end
   end
   module M
     def self.extend_object(o)
       o.class_eval do
         include N
         def self.new(*a,&b)
           r = super(*a, &b) # explicit -> less stuff to remember
           r.foo # is this what you meant?? weird.
                 # why won't X.new.foo do?
           r
         end
       end
     end
   end
   # ===== unmodified =>
   class X
     p ancestors
     extend M
     p ancestors
   end


   harp:~ > ruby a.rb
   [X, Object, Kernel]
   [X, N, Object, Kernel]


what, exactly do you mean when you say the class must not be modified?  both
the solution i posted and this one modify the class in exactly the same way :
by including a module in the class.

what you originally posted:

> given the below, if you were not allowed to modify class X
> 
> module N
>   def foo
>   end
> end
> 
> module M
>   # ...
> end
> 
> class X
>   extend M
> end
> 
> would it possible for
> 
> x = X.new
> 
> to somehow call foo as an instance method of x?

iff you really do not modify the class X, can be accomplished thus:

   harp:~ > cat a.rb
   module N
     def foo() p 42 end
   end
   module M
     include N
   end
   class X; end
   x = X.new
   x.extend M
   x.foo


   harp:~ > ruby a.rb
   42

any other way to be able to call x.foo will, in fact, modify the class X.  but
maybe that's not what you really want?

regards.

-a
-- 
be kind whenever possible... it is always possible.
- h.h. the 14th dali lama