visitor_manager.rb

class Car < CarElement
  def initialize
    # Here we build an array of objects that will be visited. This can be done
    # after initialize as well; it just needs to be built before calling 'accept'.
    @elements = []
    @elements << Wheel.new("front left")
    @elements << Wheel.new("front right")
    @elements << Wheel.new("back left")
    @elements << Wheel.new("back right")
    @elements << Body.new
    @elements << Engine.new
  end

  # go through each element and 'visit' it
  def accept(visitor)
    @elements.each do |element|
      element.accept(visitor)
    end
    visitor.visit(self)
  end
end