Extend on demand

extend_on_demand.rb

# this wont work for immediate values as Fixnum Symbols but there may be workaround
# 

module Doublable
  def self.extended(base)
    case base
      when ::Array
        base.extend Doublable::Array
      when ::String
        base.extend Doublable::String
      when ::Numeric
        base.extend Doublale::Numeric
      else
        base.extend NotDoublable
    end
  end

  module Array
    def double
      collect {|e| e.dup.extend(Doublable).double }
    end
  end

  module Numeric
    def double
      self * 2
    end
  end

  module String
    def double
      self.next 
    end
  end


  module NotDoublable
    def double
      raise "don't know how to double #{self.class} #{self.inspect}"
    end
  end
end

class MyView
  attr_reader :target
  
  def initialize(target)
    @target = target
  end

  def double
    target.dup.extend(Doublable).double
  end
end