How to pass by reference in ActionScript? - actionscript-3

Question

I'm trying to modify an Object in another class. So I have something like this:
MainClass.as:
..
var myObject:Object = new Object();
Class2_Instance.get_JSON(myObject);
trace(myObject.id); // output: undefined. whereas it should be 42. see below.
..
Class2.as
public function get_JSON(url:String , the_object:Object)
{
var request:URLRequest = new URLRequest(url);
var variables:URLLoader = new URLLoader();
variables.dataFormat = URLLoaderDataFormat.TEXT;
variables.addEventListener(Event.COMPLETE, Complete_Handler_JSON(the_object));
try
{
variables.load(request);
}
catch (error:Error)
{
trace("Unable to load URL: " + error);
}
}
function Complete_Handler_JSON(the_object:Object):Function
{
return function(event:Event):void
{
var loader:URLLoader = URLLoader(event.target);
the_object = JSON.parse(loader.data);
trace(the_object.id); //returns 42.
};
}
So the JSON operation performs correctly within Class2, and it assigns the .parse() value to the_object, but I think there is something I don't understand with AS's pass-by-reference logic. Since I was expecting myObject in MainClass.as would change, too.
What should I do to modify the value of the function argument (myObject) directly ?
Thanks !

Answer 1

The issue is in this line in your event handler:
the_object = JSON.parse(loader.data);
The minute you do this, you're no longer dealing with the object which you passed in to the method. You're assigning a new value to the local variable named the_object. It's important to understand that objects are not passed by reference - object references are passed by value. So the_object in your method is a copy of the reference. When you assign a new value, that copy is overwritten with a different reference.
The solution is to pass the reference by reference - this is related to the concept of double pointers in languages such as C++, also known as double indirection. I'm not certain that this is even possible in ActionScript.
A better solution, just return the deserialized object as a return value.

Answer 2

Objects are passed by reference.
But as i see in your code you are overwriting the_object by another one on the line : the_object=JSON.parse(loader.data).
You can create a new variable and then copy the values in the_object:
var json:Object = JSON.parse(loader.data);
for (var k:String in json) {
the_object[k]=json[k];
}