Question

Having a strong C++ background, I wonder how this works in Actionscript :

class A {

    public function callme():void {
    }

    public function foo():void {
        var a:Function = callme;
        a();
    }
}

The question is : does Actionscript “secretly” pass an object pointer alongside the function pointer?

Here is another question : is it possible to do something like this (pseudocode) :

class A {

    public function callme():void {
    }

    public function foo():void {
        var a:Function = callme;
        var classAinstance:A = new A();
        classAinstance.a();
    }
}

i.e have separate function and object pointers.

Answer 1

Yes, Flash does pass the object context along with the function pointer. This hasn’t always been the case, but is true as of ActionScript 3.0. See here:

http://www.adobe.com/devnet/actionscript/articles/actionscript3_overview.html

Method closures

Event handling is simplified in ActionScript 3.0 thanks to method closures, which provide built-in event delegation. In ActionScript 2.0, a closure would not remember what object instance it was extracted from, leading to unexpected behavior when the closure was invoked. The mx.utils.Delegate class was a popular workaround; to use it, you would write code as follows:

myButton.addEventListener("click", Delegate.create(this, someMethod));

This class is no longer needed because in ActionScript 3.0, a method closure will be generated when someMethod is referenced. The method closure will automatically remember its original object instance. Now, one can simply write:

myButton.addEventListener("click", someMethod);

As far as your second question, if you want to run a method in the context of a different object, then use .call() or .apply().

a.call(classA);

http://help.adobe.com/en_US/FlashPlatform/reference/actionscript/3/Function.html?filter_coldfusion=9&filter_flex=3&filter_flashplayer=10&filter_air=1.5