[wvxvw]

class Array2 extends Array {
	private var __len:Number = null;

	function Array2 () {
		super ();
		__len = 0;
	}
	function addItem (o:Object):Void {
		o.__uniqueID = '_'+__len;
		o.toString = function():String {
			return this.__uniqueID;
		}
		this[o] = o;
		__len++;
	}
	function removeItem (o:Object):Void {
		delete this[o];
		__len--;
	}
	public function get length ():Number {
		return __len;
	}
}

ну а если так?