gistfile1.sh

[~]$ ruby refinements.rb                                                                                                                        
refinements.rb:2: warning: Refinements are experimental, and the behavior may change in future versions of Ruby!
refinements.rb:10:in `<class:MyTestClass>': undefined method `using' for MyTestClass:Class (NoMethodError)
        from refinements.rb:9:in `<main>'

refinements.rb

module RefinementTest
  refine Hash do 
    def super_duper
      "Hello World"
    end
  end
end

class MyTestClass
  using RefinementTest

  def initialize
    puts {}.super_duper
  end
end

MyTestClass.new

Example for problem with refinements in Ruby 2.0 (see http://www.ruby-forum.com/topic/4409740)