From: Trans <transfire@...>
Date: 2008-03-02T15:35:50+09:00
Subject: Re: Using a class to extend a singleton?



On Mar 1, 4:40 pm, "Elliott Hird" <penguinoftheg...@googlemail.com>
wrote:
> On 01/03/2008, Trans <transf...@gmail.com> wrote:
>
>
>
> > Given:
>
> >   class X
> >     def yo=x; @yo=x; end
> >   end
>
> >   class Y
> >     def yo!; puts @yo; end
> >   end
>
> >   x = X.new
>
> >  Is there any way to extend x with Y's functionality (without going
> >  back and changing the given code)? Eg.
>
> >   >> x.yo="Hello World"
> >   >> x.yo!
> >   Hello World
>
> >  T.
>
> class << x; Y.instance_methods.each {|m| define_method m, Y.method(:m)}; end
>
> kind of. brings in Object onwards, though, but that's easy to fix.

Almost but not quite. You'd have to use Y.instance_method(:m) instead,
but then you get an error anyway because Y is not a subclass of X or
something to that effect.

I don't think there is any reasonable way. It's too bad. After the
discussion on MP, I decided to take a second shot at better
encapsulation of Facets. One idea was to just have a special way to
load them --if I could do the above that would work. But no go there
and nfortunately the traditional module namespaces doesn't work well
either --they can't handle aliasing of built-in methods and the double
module inclusion problem means it won't work for modules either.

Ruby really needs some fixing in this area!

To clarify the problem a faux example:

  module Facets
  module Comparable
    alias_method :gte, :>=  # no method to alias
    def ccc; "ccc"; end
  end
  end

  module Comparable
    include Facets::Comparable
  end

  10.ccc #=> NoMethodError

T.