From: trans <transfire@...>
Date: 2009-03-20T18:50:27+09:00
Subject: [ruby-core:22971] Re: [Feature #1102] Prepend Module



On Feb 7, 10:42�pm, Roger Pack <rogerdp...@gmail.com> wrote:
> > Currently when a module is included into a classes, it is appended to the class hierarchy (ie. > the method lookup order). This of course makes sense, but there are times when it would be > useful to *prepend* the module. For example:
>
> I suppose one [not too useful] hack at it could be something like
>
> class Class
> � def insert_module_at_top mod
> � � previous_ancestors = self.ancestors.select{|a| a.class == Module}
> � � include mod
> � � previous_ancestors.each{|a| include a.dup}
> � end
> end
>
> #again we have to start with a module.
>
> module Original
> � def x; '[' + super + ']'; end
> end
>
> class A
> �include Original
> end
>
> modulePrepend
> �def x; "x"; end
> end
> A.insert_module_at_topPrepend
> puts A.new.x
> => [x]
>
> Perhaps what we're saying here is we wish we could "grab" methods from
> classes, to be able to manipulate the hierarchy better? �This is
> possible with RubyParser, since you can basically get back to the
> source of the method and thus copy it around, but not afaik with 1.9

Well, that's not really the issue here. The need is to *wrap*
previously defined instance methods. If every method were defined in a
module (something I have suggested in the past actually) then it would
not be needed.

The utility comes from doing AOP-esque coding. Consider modules that
can initialize values.

  class X
  end

  module P
    attr :p
    def initialize
      @p = []
      super
    end
  end

  class X
    prepend P
  end

  X.new.p  => []

T.