public class Car  {    //內部狀態數據    public int CurentSpeed;    public int MaxSpeed;    public string name;    //汽車能不能用    private bool carIsdead;    //類構造函數    public Car() { }    public Car(string name, int currentspeed, int maxspeed = 100)    {      this.name = name;      this.CurentSpeed = currentspeed;      this.MaxSpeed = maxspeed;    }    //定義委托類型    public delegate void CarEngineHandler(string msdForCar);    //定義每個委托類型的成員變量    private CarEngineHandler listOfhandlers;    //向調用者添加注冊函數    public void RegisterWithCarEngine(CarEngineHandler methodTocall)    {      if (listOfhandlers == null)        listOfhandlers = methodTocall;      else        listOfhandlers += methodTocall;//支持多路廣播    }    //實現Accelerate()方法    public void Accelerate(int delta)    {      if (carIsdead)      {        if (listOfhandlers != null)        {          listOfhandlers("sorry,this car is dead");        }      }      else      {        CurentSpeed += delta;        //不能超過最大速度        if (5 == (MaxSpeed - CurentSpeed) && listOfhandlers != null)        {          listOfhandlers("this speed is nearly to the maxspeed");        }        if (CurentSpeed > MaxSpeed)        {          carIsdead = true;        }        else          Console.WriteLine("current speed:{0}", CurentSpeed);      }    }  }  public class Garage : IEnumerable  {    private Car[] garage = new Car[3];    public Garage()    {      garage[0] = new Car("a", 10);      garage[1] = new Car("b", 13);      garage[2] = new Car("c", 14);    }    public Enumerator GetEnumerator()    {      //返回數組對象的IEnumerator      //return garage.GetEnumerator();      //用yield關鍵字構建迭代器方法      foreach (Car c in garage)      {        //當yield return語句執行后，當前位會被        //保存下來，下一次執行會從當前位開始        yield return c;      }    }  }  class Program  {    static void Main(string[] args)    {      Garage g = new Garage();      foreach (Car c in g)      {        Console.WriteLine("car name:{0}", c.name);      }    }  }