MACROMEDIA FLEX 2-MIGRATING APPLICATIONS TO FLEX 2 User Manual download pdf (Page 39)

Miscellaneous 39

__proto__

ActionScript 3.0 does not support “hacking” the prototype chain. The use of __proto__ is no

longer supported. For example:

ActionScript 2.0:

Class A {}

var a: A = new A;

trace(a.b) // Output: undefined

a.__proto__.b = 10 // Ok

trace(a.b) // Output: 10

class C {

var x:Number = 20;

}

var c:C = new C();

a.__proto__ = C.prototype;

trace(a.x); // Output: 20

ActionScript 3.0:

class A {}

var a: A = new A

trace(a.b) // Output: undefined

a.__proto__.b = 10 // Error, __proto__ unsupported.

// Use .constructor.prototype instead.

a.constructor.prototype.b = 10; // Ok

trace(a.b) // Output: 10

class C {

var x:Number = 20;

}

var c:C = new C();

a.__proto__ = C.prototype; // Error, __proto__ unsupported.

// .constructor.prototype is equivalent,

// though read only.

Primitive types

Primitive types are sealed classes and do not have object wrappers. Primitive types in

ActionScript 3.0 are final, sealed classes. Furthermore, there are no object wrappers for

primitives. As a result, you cannot create properties on them at run time; for example:

ActionScript 2.0:

newstring = new String("hello");

newstring.sayHi = function() {

trace("hi!");

}

newstring.sayHi();

newstring2 = "hello";

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MACROMEDIA FLEX 2-MIGRATING APPLICATIONS TO FLEX 2 User Manual Page 39