public class User        {//使用省缺参数，一般不需要再为多态做各种静态重载了public User( string name = "anonym", string type = "user" )                {this.UserName = name;this.UserType = type;                 }public UserName { private set; get; }public UserType { private set; get; }        }User user = new User();  //不带任何参数实例化Console.WriteLine( user.UserName );  //输出 anonymConsole.WriteLine( user.UserType );    //输出 user// dynamic 关键字可以绕过静态语言的强类型检查dynamic d = user;Console.WriteLine( d.UserName );      //输出 anonymConsole.WriteLine( d.UserType );        //输出 user// ExpandoObject 是一个特殊对象,包含运行时可动态添加或移除的成员dynamic eo = new System.Dynamic.ExpandoObject();        eo.Description = "this is a dynamic property";Console.WriteLine( eo.Description );    // 输出 this is a dynamic property//继承 DynamicObject 类，重写 TryInvokeMember 虚拟方法public class Animal : DynamicObject        {//尝试执行成员，成功返回 true，并从第二个参数输出执行后的返回值public override bool TryInvokeMember( InvokeMemberBinder binder, object[] args, out object result)               {bool success = base.TryInvokeMember( binder, args, out result);//基类尝试执行方法，返回 false，表示方法不存在，out 输出 null 值//if (! success)  result = null;//若返回 false 将抛出异常return true;               }        }//派生动态类public class Duck : Animal        {public string Quack()              {return "Quack!!";              }        }//派生动态类public class Human : Animal        {public string Talk()              {return "Talk!!";              }         }//调用动态方法public static string DoQuack( dynamic animal )        {string result = animal.Quack();return result ?? "Null";  //(result == null)? "Human" : result;         }var duck = new Duck();var human = new Human();Console.WriteLine( DoQuack( duck ) );      //输出 QuackConsole.WriteLine( DoQuack( human ) );   //输出 Null , Human类不包含Quack方法，执行失败

C# 4 dynamic 动态对象 动态类型转换