class Drill
  attr_reader :channel

  def initialize(channel)
    @channel = channel
    @started = false
  end

  def start!
    @started = true
  end

  def started?
    @started
  end

  def exists?
    true
  end

  class Empty < Drill
    def initialize
      super(nil)
    end

    def start!; end

    def exists?
      false
    end
  end
end