gistfile1.rb

# GoKart becomes a module
module GoKart

  # GoKart.new becomes a factory method for strategy classes
  def self.new( strategy = nil )
    ( strategy == :reverse ) ? ReverseStrategy.new : ForwardStrategy.new
  end

  class ForwardStrategy
    def drive
      puts "Forward"
    end
    def stop
      puts "Stop"
    end
  end

  class ReverseStrategy < ForwardStrategy
    def drive
      puts "Reverse"
    end
  end

end

# No interface change for consumer:

k = GoKart.new
k.drive
k.stop

k = GoKart.new( :reverse )
k.drive
k.stop