A cleaner way to decorate all methods in a module

decorate_module.rb

module Decorator

  def self.decorate(target_klass, include_module, decorator_method)
    proxy = Class.new { include include_module }.new

    target_klass.class_eval do
      include_module.instance_methods.each do |name|
        undecorated_method = proxy.method(name)

        define_method(name) do |*args, &block|
          send(decorator_method, undecorated_method, *args, &block)
        end
      end
    end
  end

end

module PlainOldRubyMethods
  def exclaim!(value)
    value.to_s + '!'
  end

  def map_words(sentence, separator, &block)
    sentence.split(' ').collect { |word| yield word }.join(separator)
  end
  alias :scramble :map_words
end

class MethodChain
  # Decorate all methods in the PlainOldRubyMethods module with the :chainable method
  # and define them on this class.
  Decorator.decorate self, PlainOldRubyMethods, :chainable

  def chainable(undecorated_method, *args, &block)
    @chain << undecorated_method.call(@chain.last, *args, &block)
    self
  end

  def initialize(value)
    @chain = [value]
  end

  def finish
    @chain.last
  end
end

# A simple example:
chain = MethodChain.new('ouch')
puts 'exclaim: ' + chain.exclaim!.finish

# Blocks, arguments, and aliased methods all work as expected:
chain = MethodChain.new('what am I saying?')
puts 'scramble: ' + chain.scramble('-') { |word| word.reverse }.finish

output.txt

$ ruby decorate_module.rb 
exclaim: ouch!
scramble: tahw-ma-I-?gniyas

Inspired by http://yehudakatz.com/2009/07/11/python-decorators-in-ruby/ and https://github.com/wycats/ruby_decorators/blob/master/decorators.rb