is VS as operator

is: return true or false

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication6
{
    abstract class Purchasedable
    {

    }
    abstract class Moveable : Purchasedable
    {

    }
    abstract class Car : Moveable
    {
        abstract public void Talk();
        public void Drive()
        {
            Console.WriteLine("WROOOOOOM");
        }
        public virtual void TruboBosst()
        {
            Console.WriteLine("Styuff and things!");
        }
    }
    class Car1 : Car
    {
        public override void Talk()
        {

        }
    }
    class Program
    {
        static void Main(string[] args)
        {
            var objects = new List<object>();   //object是所有类型的基类
            objects.Add(10);
            objects.Add("Shawn's car");
            objects.Add(new Car1());

            foreach (var item in objects)
            {
                if (!(item is Purchasedable)) //Item不是Purchaseable的话就跳出
                {
                    continue;
                }
                var purchaseable = (Purchasedable)item; //比较as方法
                Console.WriteLine("Do you want to purchase item {0}", purchaseable);
            }
            Console.ReadLine();
        }
    }
}

as:可以做的更多，return item type or null

 class Program
    {
        static void Main(string[] args)
        {
            var objects = new List<object>();   //object是所有类型的基类
            objects.Add(10);
            objects.Add("Shawn's car");
            objects.Add(new Car1());

            foreach (var item in objects)
            {
                var purchaseable = item as Purchasedable;//if item is purchaseable return purchaseable type, if not return null
                if (purchaseable == null)
                    continue;
                Console.WriteLine("Do you want to purchase item {0}", purchaseable);
            }
            Console.ReadLine();
        }
    }

注意：is and as不返回reception，不像cast operator