[flexcoders] how do I set the default value for an array in a function definition?

[luvfotography]

How do I make the array parameter optional??

private function howdoI(mycount:int,mystring:String, myArray:Array = []):void {
trace('hellow');
}

I get 
1047: Parameter initializer unknown or is not a compile-time constant.   


How do I make the Array parameter optional? :
myArray:Array = []

thanks,