Simple Decorator Using Ruby Delegate for Ruby 2.1.5 & Rails 4

decorator.rb

module Project
  module Decorators

    module Draperize
      def self.included _klass
        _klass.class_eval  { extend ClassMethods }
      end

      module ClassMethods
        # Initialize a new decorator instance by passing in
        # an instance of class `_klass`.
        #
        # When passing in a single object, using `.decorate` is
        # identical to calling `.new`.
        def decorate(component)
          new(component)
        end
      end
    end

    require 'delegate'

    class Base < SimpleDelegator
      def initialize(component)
        super
        @component = component
      end

      def class
        __getobj__.class
      end
    end

    class ProductDecorator < Base
      include Draperize

      # Add methods to decorate `component`
      def decorated?
        "Why, yes! Here's your decorated product '#{name}' (#{@component})"
      end
    end

  end
end

class Product
  def initialize
    @name = "SPAM!"
  end
  attr_reader :name
end

p = Product.new
dp = Project::Decorators::ProductDecorator.decorate(p)

puts "p methods: #{p.methods.count}\n"
puts "dp methods: #{dp.methods.count}\n"
extra_methods = ((p.methods | dp.methods) - (p.methods & dp.methods))
puts "Decorated methods in dp: #{extra_methods.inspect}\n"
puts "Calling dp#decorated?: #{dp.decorated?}\n"
puts "dp class: #{dp.class}\n"

foo@localhost [18:53:24] code/ruby {2.1.5}
-> % ruby decorator.rb
p methods: 56
dp methods: 62
Decorated methods in dp: [:decorated?, :__getobj__, :__setobj__, :method_missing, :marshal_dump, :marshal_load]
Calling dp#decorated?: Why, yes! Here's your decorated product 'SPAM!' (#<Product:0x007fd29909f650>)
dp class: Product

References

1. https://robots.thoughtbot.com/evaluating-alternative-decorator-implementations-in
2. http://blog.codeclimate.com/blog/2012/10/17/7-ways-to-decompose-fat-activerecord-models/
3. https://blog.engineyard.com/2014/keeping-your-rails-controllers-dry-with-services

Thanks

To David (@workmad3) for spotting an obvious blunder on my part!