actionscript3 Error: Attempt to delete the fixed property loader. Only dynamica

Error: Attempt to delete the fixed property loader.  Only dynamically defined properties can be deleted.

查阅相关资料才知道在actionscirpt 3 中delete只能删除动态类中动态声明的属性。

在actionscirpt 3中开始支持运行时sealed class，没有用dynamic关键字声明的类都是sealed class(这里要避免和C#里的sealed关键字混淆，c#里的sealed关键字表示这个类无法被继承)。sealed class(或者他的实例)都无法在运行时添加或者删除他们定义的属性。因此按照ECMAScript规范，delete将只能删除动态类动态创建的属性，甚至无法删除方法级的变量。

如果试图用delete关键字删除动态属性以外的东西，将得到一个编译时错误（strict mode），看起来想这样：

Error: Attempt to delete the fixed property loader.  Only dynamically defined properties can be deleted.

在as3中，delete关键字会返回一个bool值来标识操作是否成功。（如果成功，那么这个属性将不再存在）

可以编写以下这样的代码来测试

var t:* = new Timer(15); 
trace(delete(t.delay)); // traces false, object is sealed so can't delete
trace(t.delay); // 15 - delete never occurred
var o:* = {fun:"stuff"};
trace(delete(o.fun)); // traces true, object is dynamic so can delete
trace(o.fun); // undefined - delete occurred
trace(delete(o.foo)); // true, because foo is not defined after delete