OOP question

I was wondering if you could do something like this in AS3:

 
package {
public class something {
public function something {
//...
//...
  this.addEventListener(Event.COMPLETE, callFunction);
}
public function callFunction(evt:Event):void {
 
}
}
 
}
 

and then in the flash movie customize that callFunction like in as2:

 
var blah:something = new something();
blah.callFunction = function() {
//code
}

or do i have to dispatch an event in the class and then in the flash add a listener for that event and make my own function…
But that just seems like an extra step.