使用转换运算符

http://msdn.microsoft.com/zh-cn/library/85w54y0a(VS.80).aspx

//卡车
    class Truck
    {
        public Truck()
        {
            Desc = "卡车";
        }

        string _desc;

        public string Desc
        {
            get { return _desc; }
            set { _desc = value; }
        }

        public static explicit operator Truck(Car c)
        {
            Truck t = new Truck();
            t.Desc = c.Desc;
            return t;
        }

    }

    //轿车
    class Car
    {
        public Car()
        {
            Desc = "轿车";
        }

        string _desc;

        public string Desc
        {
            get { return _desc; }
            set { _desc = value; }
        }

        public static implicit operator Car(Truck t)
        {
            Car c = new Car();
            c.Desc = t.Desc;
            return c;
        }
    }

//调用
class Program
    {
        static void Main(string[] args)
        {
            Truck t = new Truck();
            Car c = new Car();
            Console.WriteLine("Truck:" + t.Desc);
            Console.WriteLine("Car:" + c.Desc);

            Console.WriteLine("explicit and implicit");

            Truck t1 = (Truck)c;
            Car c1 = t;
            Console.WriteLine("Truck:" + t1.Desc);
            Console.WriteLine("Car:" + c1.Desc);
        }
    }