Question

I have found some code that uses the virtual keyword for functions, like:

package tryOut{
    public class Parent {

        public function Parent() {}

        public function foo():void{
            trace("Parent foo");
        }//foo

        public virtual function bar():void{
            trace("Parent virtual bar");
        }//bar      
    }//class
}//package

As far as I understand using the virtual keyword should modify the way overriding a method works, or the way using a child method would work, or something. But it seems it does nothing at all. Having the extention:

package tryOut {
    public class Child extends Parent {
        public function Child() {}

        public override function foo():void {
            trace("Child foo");
        }//foo

        public override function bar():void {
            trace("Child virtual bar");
        }//bar

    }//class
}//package

The following code prints:

var parent:Parent = new Parent();
var child:Child = new Child();

parent.foo(); //Parent foo
child.foo(); //Child foo
parent.bar(); //Parent virtual bar
child.bar(); //Child virtual bar

var childCast:Parent = child as Parent;

parent.foo(); //Parent foo
childCast.foo(); //Child foo
parent.bar(); //Parent virtual bar
childCast.bar(); //Child virtual bar

So both methods work the same regarding the override. Does the virtual keyword changes something I am missing?

Answer 1

From the help documents (If you’re using Flash, do a search for ‘virtual’):

There are also several identifiers
that are sometimes referred to as
future reserved words. These
identifiers are not reserved by
ActionScript 3.0, though some of them
may be treated as keywords by software
that incorporates ActionScript 3.0.
You might be able to use many of these
identifiers in your code, but Adobe
recommends that you do not use them
because they may appear as keywords in
a subsequent version of the language.

abstract boolean byte cast

char debugger double enum

export float goto intrinsic

long prototype short synchronized

throws to transient type

virtual volatile

So in AS3, virtual does absolutely nothing.