C#中关键字ref修饰类对象或结构体[转]

using System;
using System.Collections.Generic;
using System.Text;
namespace CSharpTest
{
    struct Dog 
    {
        public int _nFeet;
        public string _sound;
        public Dog(int n, string sound)
        {
            _nFeet = n;
            _sound = sound;
        }
        public int NFeet
        {
            get { return _nFeet; }
            set { _nFeet = value; }
        }
        public string Sound
        {
            get { return _sound; }
            set { _sound = value; }
        }
        public string ToString()
        {
            return String.Format("The dog has {0} feet, and sounds {1}.",
                _nFeet.ToString(), _sound);
        }
    }
    class Cat
    {
        private int _nFeet;
        private string _sound;
        public Cat(int n, string sound)
        {
            _nFeet = n;
            _sound = sound;
        }
        public int NFeet
        {
            get { return _nFeet; }
            set { _nFeet = value; }
        }
        public string Sound
        {
            get { return _sound; }
            set { _sound = value; }
        }
        public string ToString()
        {
            return String.Format("The cat has {0} feet, and sounds {1}.",
                _nFeet.ToString(), _sound);
        }
    }
    class Program
    {
        static void Main(string[] args)
        {
            // Cat
            Cat cat = new Cat(4, "miao~");
            System.Console.WriteLine(cat.ToString());
            BeatCat(cat);
            System.Console.WriteLine(cat.ToString());
            BeatCat2(ref cat);
            System.Console.WriteLine(cat.ToString());
            System.Console.WriteLine();
            // Dog
            Dog dog = new Dog(4, "wang!");
            System.Console.WriteLine(dog.ToString());
            BeatDog(dog);
            System.Console.WriteLine(dog.ToString());
            BeatDog2(ref dog);
            System.Console.WriteLine(dog.ToString());
        }
        public static void BeatCat(Cat cat)
        {
            cat.NFeet = 3;
            cat.Sound = "wang~";
        }
        public static void BeatCat2(ref Cat cat)
        {
            cat.NFeet = 2;
            cat.Sound = "huhu~";
        }
        public static void BeatDog(Dog dog)
        {
            dog.NFeet = 3;
            dog.Sound = "miao!";
        }
        public static void BeatDog2(ref Dog dog)
        {
            dog.NFeet = 2;
            dog.Sound = "huhu!";
        }
    }
}