在不继承的情况下扩展类的方法

using System;

namespace TTest
{
    class Program
    {
        static void Main(string[] args)
        {
            string s = "abcdefg";
            Console.WriteLine(s.StrExt());

            ClassA ca = new ClassA();
            ca.Fun1();
            ca.Fun2();

            Console.Read();
        }

    }

    //扩展string类
    public static class StringExtensions
    {
        public static string StrExt(this string str)
        {
            return str + "@Ext";
        }
    }

    public class ClassA
    {
        public void Fun1()
        {
            Console.WriteLine("Fun1");
        }
    }

    //扩展ClassA类
    public static class ClassAExtensions
    {
        public static void Fun2(this ClassA a)
        {
            Console.WriteLine("Fun2");
        }
    }
}

运行测试