From: Trans <transfire@...>
Date: 2007-03-16T07:20:01+09:00
Subject: Re: General Ruby OOP Question - using inheritance or include for shared attributes



On Mar 15, 11:25 am, james.d.mast...@gmail.com wrote:
> On Mar 15, 12:11 am, "Trans" <transf...@gmail.com> wrote:
>
> >   module X; def self.x; "x"; end; end
> >   class Y; include X; end
> >   Y.x  #=> error
>
> > IMHO It's unfortunate that this is the case --or at least that there's
> > not a method other than #include that can do it. I guess it's because
> > I wrote annotations, which turned out to be very tricky b/c of this.
>
> In the case of pulling in module methods as class (singleton) methods,
> you can use extend instead of include.  Your second example rewritten
> with "extend" would work:
>
> module X; def x; "x"; end; end
> class Y; extend X; end
> Y.x  #=> "x"
>
> Unfortunately, I'm fairly sure that would require separate modules for
> class methods (through extend) and instance methods (through include).

Have a look at module/class_extension in Facets. This sophisticated
code was developed by Daniel Schierbeck with the help of a number of
people including myself, Nobu Nakada, Ulysses and Matz.


class Module

 
alias_method :append_features_without_class_extension, :append_features

  # = class_extension
  #
  # Normally when including modules, class/module methods are not
  # extended. To achieve this behavior requires some clever
  # Ruby Karate. Instead class_extension provides an easy to use
  # and clean solution. Simply place the extending class methods
  # in a block of the special module method #class_extension.
  #
  #   module Mix
  #     def inst_meth
  #       puts 'inst_meth'
  #     end
  #
  #     class_extension do
  #       def class_meth
  #         "Class Method!"
  #       end
  #     end
  #   end
  #
  #   class X
  #     include Mix
  #   end
  #
  #   X.class_meth  #=> "Class Method!"
  #

  def class_extension(&block)
    @class_extension ||= Module.new do
      def self.append_features(mod)
        append_features_without_class_extension(mod)
      end
    end
    @class_extension.module_eval(&block) if block_given?
    @class_extension
  end

  private :class_extension

  def append_features(mod)
    append_features_without_class_extension(mod)
    mod.extend(class_extension)
    if mod.instance_of? Module
      mod.__send__(:class_extension).__send__(:include,
class_extension)
    end
  end

end

class Class
  undef_method :class_extension
end


T.