ActionScript 3：构造函数必须是实例方法

Question

我使用的是在stackoverflow.com上的另一个页面中找到的一段代码

package
{
    import flash.display.MovieClip;
    import flash.events.Event;
    import flash.events.MouseEvent;

    public class Guest extends MovieClip
    {
        var walkSpeed:Number = 5;
        var oldPosX;
        var oldPosY;

        public function Guest()
        {
            stage.addEventListener(MouseEvent.CLICK, walk);
        }

        function walk(event: MouseEvent):void
        {
            oldPosX = parent.mouseX;
            oldPosY = parent.mouseY;
            rotation = Math.atan2(oldPosY - y, oldPosX - x) / Math.PI * 180;
            addEventListener(Event.ENTER_FRAME, loop);
        }

        function loop(event: Event):void
        {
            // see if you're near the target
            var dx:Number = oldPosX - x;
            var dy:Number = oldPosY - y;
            var distance: Number = Math.sqrt((dx * dx) + (dy * dy));

            if (distance < walkSpeed)
            {
                // if you are near the target, snap to it
                x = oldPosX;
                y = oldPosY;
                removeEventListener(Event.ENTER_FRAME, loop);
            }
            else
            {
                x = x + Math.cos(rotation / 180 * Math.PI) * walkSpeed;
                y = y + Math.sin(rotation / 180 * Math.PI) * walkSpeed;
            }
        }
    }
}

此特定行（第2行）发生错误：

    import flash.display.MovieClip;

我认为我的案例是独一无二的，因为当我查阅时，人们会说这是一个命名冲突。你有什么想法吗？