使用接口改变已经装箱的值类型的字段。

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

namespace App1
{
    struct Point
    {
        public Int32 x, y;
        public void Change(Int32 x, Int32 y)
        {
            this.x = x;
            this.y = y;
        }
        public override string ToString()
        {
            //return base.ToString();
            return string.Format("{0},{1}", x, y);
            //return string.Format("{0},{1},{2}", x, y, x);
        }
    }
    class Program
    {
        static void Main(string[] args)
        {
            Point p = new Point();
            p.x = p.y = 1;
            Console.WriteLine(p);
            //调用p的ToString()方法,若不override---ToString()则输出"App1.Point"
            ///////////////////////////
            p.Change(2, 2);
            Console.WriteLine(p);
            ///////////////////////////
            object o = p;//p装箱
            Console.WriteLine(o);//o指向装箱后的p---(2,2)
            //////////////////////////
            ((Point)o).Change(3, 3);//把o拆箱到临时栈上,并在临时栈上改变Point的值成(3,3)
            Console.WriteLine(o);//输出原来o指向的对象的值:(2,2)
            Console.Read();
        }
    }
}

****************************************

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

namespace App1
{
    interface IChangeBoxedPoint
    {
        void Change(Int32 x, Int32 y);
    }
    struct Point:IChangeBoxedPoint
    {
        public Int32 x, y;
        //现在该Change方法成了实现的接口的方法
        public void Change(Int32 x, Int32 y)
        {
            this.x = x;
            this.y = y;
        }
        public override string ToString()
        {
            //return base.ToString();
            return string.Format("{0},{1}", x, y);
            //return string.Format("{0},{1},{2}", x, y, x);
        }
    }
    class Program
    {
        static void Main(string[] args)
        {
            Point p = new Point();
            p.x = p.y = 1;
            Console.WriteLine(p);
            //调用p的ToString()方法,若不override---ToString()则输出"App1.Point"
            ///////////////////////////
            p.Change(2, 2);
            Console.WriteLine(p);
            ///////////////////////////
            object o = p;//p装箱
           
            Console.WriteLine(o);//o指向装箱后的p---(2,2)
            //////////////////////////
            ((Point)o).Change(3, 3);//把o拆箱到临时栈上,并在临时栈上改变Point的值成(3,3)
            Console.WriteLine(o);//输出原来o指向的对象的值:(2,2)
            ///////////////////////////
            ((IChangeBoxedPoint)p).Change(4,4);//把p装箱,改变已装箱对象,随后将之丢弃
            Console.WriteLine(p);//输出p(2,2)
            //////////////////////////
            ((IChangeBoxedPoint)o).Change(5, 5);//这里o本身即是已装箱的对象,把它改变
            Console.WriteLine(o);//输出刚刚被改变的o(5,5)

            Console.Read();
        }
    }
}