var COUNT:int = 10;

var a:Array = new Array( COUNT ); //Vector.<Number> = Vector.<Number>( new Array( COUNT ));
//a.fixed = true;

var writeTo:Object;

var i:int;

while ( i < COUNT )
{
	writeTo = a[ i ]; //testing that we indeed have access to the index
	a[ i ] = Math.random();
	writeTo = a[ i++ ];
}

while ( i >= 0 )
{
	a.pop(); //if a is a Vector, this will throw a run-time error
	i--;
}

var COUNT:int = 10;

var a:Array = new Array( COUNT ); //Vector.<Number> = Vector.<Number>( new Array( COUNT ));
var writeTo:Object;

var i:int;

while ( i < COUNT )
{
	writeTo = a[ i ]; //testing that we indeed have access to the index
	a[ i ] = Math.random();
	writeTo = a[ i++ ];
}

while ( i >= 0 )
{
	a.pop();
	i--;
}

no fixed length Arrays in as3

array

ActionScript 3