If Iterator::valid() returns false, the foreach() loop will be terminated.
(PHP 5, PHP 7, PHP 8)
Iterator::valid — 检查当前位置是否有效
此函数没有参数。
返回将被转换为bool 。成功时返回 true， 或者在失败时返回 false。
If Iterator::valid() returns false, the foreach() loop will be terminated.If your class implements also ArrayAccess interface, you could use as valid() body
function valid(){
return $this->offsetExists($this->position);
}