From: Trans <transfire@...>
Date: 2006-12-11T01:44:53+09:00
Subject: Re: bending ruby space


ara.t.howard@noaa.gov wrote:
> On Sun, 10 Dec 2006, Trans wrote:
>
> > i came upon this "pattern" working on a rather difficult problem. see
> > if you can wrap your head around this bending of ruby space and what it
> > might be good for.
> >
> >  module R; end
> >  module U; include R; end
> >  module R; extend U; end
>
> one side effect is that all instance methods of R are available at the module
> level too.  i generally do that this way:
>
>    harp:~ > cat a.rb
>    class Module
>      def export meth
>        module_function meth
>        public meth
>      end
>    end
>
>    module R
>      def foo() 42 end
>      export :foo
>    end

that's an interesting method in it's own right. i'm tempted to add to
facets, though maybe the name isn't the best. I say that only b/c I've
been using #import to load a lib directly into the current module
space. and it would seem to me #import and #export should have some
related usage --one way or the other.

in any case you all are partly right of course. but the neat part of
this  --the real "bending" and the reason it uses two modules the way
it does....

  module R; end
  module U; include R; end
  module R; extend U; end

  module R
    def x; "x"; end
  end

  module U
    def x; "{" + super + "}"; end
  end

  R.x  #=> "{x}"

the effect is *dynamic* AOP wrapping of R by U. it is dynamic b/c it is
possible to define the "aspect" U prior to any corresponding method in
R. (btw, 'if  defined?(super)' is helpful in such cases). I used this
myself to cache specifically named methods that may, or may not, be in
a user-defined code snippet.
it is unfortuate however that, afaict, the same pattern can't be used
on a class --just a module.

t.