C#使用yield关键字构建迭代器详解

以前，如果我们希望构建支持foreach枚举的自定义集合，只能实现IEnumerable接口（可能还有IEnumerator()）,返回值还必须是IEnumerator类型，除此之外还可以通过迭代器来使用构建foreach循环的类型，详细见下链接。

 代码

 public class Car
  {
    //内部状态数据
    public int CurentSpeed;
    public int MaxSpeed;
    public string name;
    //汽车能不能用
    private bool carIsdead;
    //类构造函数
    public Car() { }
    public Car(string name, int currentspeed, int maxspeed = 100)
    {
      this.name = name;
      this.CurentSpeed = currentspeed;
      this.MaxSpeed = maxspeed;
    }
    //定义委托类型
    public delegate void CarEngineHandler(string msdForCar);
    //定义每个委托类型的成员变量
    private CarEngineHandler listOfhandlers;
    //向调用者添加注册函数
    public void RegisterWithCarEngine(CarEngineHandler methodTocall)
    {
      if (listOfhandlers == null)
        listOfhandlers = methodTocall;
      else
        listOfhandlers += methodTocall;//支持多路广播
    }
    //实现Accelerate()方法
    public void Accelerate(int delta)
    {
      if (carIsdead)
      {
        if (listOfhandlers != null)
        {
          listOfhandlers("sorry,this car is dead");
        }
      }
      else
      {
        CurentSpeed += delta;
        //不能超过最大速度
        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()
    {
      //返回数组对象的IEnumerator
      //return garage.GetEnumerator();
      //用yield关键字构建迭代器方法
      foreach (Car c in garage)
      {
        //当yield return语句执行后，当前位会被
        //保存下来，下一次执行会从当前位开始
        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);
      }
    }
  }

参考：C#中可枚举类型详解

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