gistfile1.rb

module Drivable
  extend ActiveSupport::Concern
  class TemplateError < RuntimeError; end
 
  included
    validates :direction, :presence => true
    validates :speed, :presence => true
  end
  
  def turn(new_direction)
    self.direction = new_direction
  end
  
  def brake
    self.speed = 0
  end
  
  def accelerate
    self.speed = [speed + acceleration, top_speed].min
  end
  
  def top_speed
    raise TemplateError, "The Drivable module requires the " +
                         "including class to define a " +
                         "top_speed method"
  end
  
  def acceleration
    raise TemplateError, "The Drivable module requires the " +
                         "including class to define an " +
                         "acceleration method"  
  end
end