Nullify object passed to a function

Question

I have the following problem with objects in actionscript3:

var o:Object = new Object();
destroyObject(o);
trace(o); // [object Object]

function destroyObject(obj:Object):void{
   obj = null; 
   trace(obj); // null
}

Since objects are passed by reference in AS3 I assume that the previous code would change o to null, but it doesn't. Could someone explain me 'why'?

Thanks.

Answer 1

Objects are passed by reference, but the reference itself is passed by value. The statement obj = null sets the parameter obj to null, which means that obj no longer references the object, but the object itself is still present, and is still referenced by the variable o when destroyObject returns.