gistfile1.rb

# Slight modifications to code posted by Gregory Brown at http://pastie.org/515450
require 'delegate'

module Decoration
  def decorator_for(*types, &block)
    types.each do |type|
      decorators[type] = Module.new(&block)
    end
  end

  def decorators
    @decorators ||= {}
  end

  def decorate(target)
    obj = SimpleDelegator.new(target)
    
    # walk in reverse order so most specific patches get applied LAST
    target.class.ancestors.reverse.each do |a|
      if decorators[a]
        obj.extend(decorators[a]) 
      end
    end
    
    return obj
  end
end

class MyView
  
  extend Decoration
  attr_reader :target
  
  decorator_for Numeric, String do
    def double
      self * 2
    end
  end

  decorator_for Symbol do
    def double
      (self.to_s * 2).to_sym
    end
  end

  decorator_for Array do
    def double
      map { |o| MyView.new(o).double }
    end
  end
  
  decorator_for Hash do
    def double
      h = {}
      self.each { |key, val| h[MyView.new(key).double] = MyView.new(val).double }
      h
    end
  end
 
  decorator_for Object do
    def double
      raise "Don't know how to double #{self.inspect}"
    end
  end

  def initialize(target)
    @target = self.class.decorate(target)
  end

  def double 
    target.double
  end

end

p MyView.new('aaa').double
p MyView.new(49).double
p MyView.new(:a).double
p MyView.new(['b', 6]).double
p MyView.new({:a => 1}).double

class MyCollaborator
  def double
    'MyCollaborator#double'
  end
end

p MyView.new(MyCollaborator.new).double