decorator pattern that defines the method the first time it delegates

model_decorator.rb

class ModelDecorator

  module Decorated

    def self.extended(base)
      base.send(:include, InstanceMethods)
    end

    def decorate(object)
      @decorated_object ||= object
    end

    def decorated_object
      @decorated_object
    end

    module InstanceMethods

      def decorated
        instance_variable_get "@#{self.class.decorated_object}".to_sym
      end
    end
  end

  extend Decorated


  def method_missing(method_name, *args, &block)
    if decorated.respond_to?(method_name)
      self.class.class_eval %Q[
          def #{method_name}(*args, &block)
            decorated.send(:#{method_name}, *args, &block)
          end
        ]
      send(method_name, *args, &block)
    else
      raise NoMethodError, "Decorated object #{decorated} does not implement #{method_name}"
    end
  end
end

class DecoratedPerson < ModelDecorator

  decorate :person

  def initialize(person)
    @person = person
  end
end