From: Sam Roberts <vieuxtech@...>
Date: 2008-05-06T15:00:13+09:00
Subject: delegation question, where I want prototype style delegation

I want to make an object that behaves like another object would, if that
object had had it's #each method redefined.

I can do this with extend(), but that permanently damages the object.

I can do it with delegate/method_missing, except I need to reimplement
every method of the delegatee, which sucks.

I could do this in prototype based languages, where you can effectively
create a new object that behaves like another object with a few differences,
but don't see a way in an OO language like ruby.

Below is an example of what I want to do, implemented with extend.

But it has a problem,  it modifies the target object, but I may want
to create mutiple delegates to the
target, each with a different set of "views", that behave like the
target object would if it
had its #each method redefined.

Btw, what I'm actually doing is I have a calendar object, and I want
to create various views
of the calendar, ones including events but not todos, ones that appear
to only have
components that occur in a particular period, etc.

class Base
  include Enumerable

  def initialize(ary)
    @ary = ary.to_a
  end

  def each
    @ary.each{|a| yield a}
  end

  def show
    inject("show: ") {|accum, o| accum + o.to_s + ","}
  end
end

module Negate
  def each(&block)
    super do |a|
      yield -a
    end
  end
end

module Add10
  def each(&block)
    super do |a|
      yield a+10
    end
  end
end

o = Base.new(1..3)
o.extend Negate.dup
o.extend Add10
o.extend Negate.dup

o.each {|_| puts _ }

puts o.show