class Driver
  attr_reader :car

  def initialize
    @car ||= Car.new
  end

  def floor_it
    car.accelerate_to(120)
  end
end

class Car
  def initialize
    # some setup here
  end

  def accelerate_to(target_speed)
    while target_speed > current_speed
      # go faster
    end
  end

  # lots of other car stuff
end