FuelTank.rb

module FuelTank
  def fill_tank(level)
    self.fuel_tank = level
  end
 
  def fuel_level
    self.fuel_tank
  end
 
protected
attr_accessor :fuel_tank
end
  
class Car
  include FuelTank
  attr_reader :current_rpm
 
  @@instances =0
 
  def self.instances
    @@instances
  end
 
  def self.debug(log)
    puts "!!!DEBUG: #{log }!!!!!"
  end
 
  debug "start interface"
 
  def initialize
    @current_rpm = 0
    @@instances += 1
  end
  
  def start_engine
    start_engine! if engine_stopped?
  end

  def engine_stopped?
    current_rpm.zero?
  end

  debug  " end interface"

  protected

  attr_writer :current_rpm

  def initial_rpm
    700
  end

  def start_engine!
    self.current_rpm =initial_rpm
  end
 
    #остановить двигатель
end
 
class Bike
  include FuelTank
end