C# 4 dynamic 動態對象 動態類型轉換

public class User
        {
//使用省缺參數，一般不需要再為多態做各種靜態重載了
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();  //不帶任何參數實例化
Console.WriteLine( user.UserName );  //輸出 anonym
Console.WriteLine( user.UserType );    //輸出 user

// dynamic 關鍵字可以繞過靜態語言的強類型檢查
dynamic d = user;
Console.WriteLine( d.UserName );      //輸出 anonym
Console.WriteLine( d.UserType );        //輸出 user

// ExpandoObject 是一個特殊對象,包含運行時可動態添加或移除的成員
dynamic eo = new System.Dynamic.ExpandoObject();
        eo.Description = "this is a dynamic property";
Console.WriteLine( eo.Description );    // 輸出 this is a dynamic property

//繼承 DynamicObject 類，重寫 TryInvokeMember 虛擬方法
public class Animal : DynamicObject
        {
//嘗試執行成員，成功返回 true，並從第二個參數輸出執行后的返回值
public override bool TryInvokeMember( InvokeMemberBinder binder, 
object[] args, out object result)
               {
bool success = base.TryInvokeMember( binder, args, out result);
//基類嘗試執行方法，返回 false，表示方法不存在，out 輸出 null 值
//if (! success)  result = null;
//若返回 false 將拋出異常
return true;
               }
        }

//派生動態類
public class Duck : Animal
        {
public string Quack()
              {
return "Quack!!";
              }
        }

//派生動態類
public class Human : Animal
        {
public string Talk()
              {
return "Talk!!";
              }
         }

//調用動態方法
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 ) );      //輸出 Quack
Console.WriteLine( DoQuack( human ) );   //輸出 Null , Human類不包含Quack方法，執行失敗