decorating.rb

module Decorating
  def decorate(meth_id, *modules)
    alias_method("__#{meth_id}__", meth_id)
    define_method(meth_id) do |*args|
      result = send("__#{meth_id}__", *args)
      modules.each { |m| result.extend(m) }
      return result
    end
  end
  
  def ddef(meth_id, *mods, &block)
    define_method(meth_id) do |*args|
      result = block.call(*args)
      mods.each { |m| result.extend(m) }
      return result
    end
  end
end

Object.send(:include, Decorating)

module Summable
  def sum
    inject(0) { |s, e| s + e }
  end
end

module Title
  def titleize
    downcase.gsub(/\s+/, "-").gsub(/[^a-z0-9-]/, "")
  end
end

class Account
  ddef(:balances, Summable) do |*args|
    [1, 2, 3]
  end
end

class Movie
  def title
    "It's A Wonderful Life"
  end
  
  decorate :title, Title
end

acct = Account.new
puts acct.balances.sum

movie = Movie.new
puts movie.title.titleize