Notice if you call it with open empty generator, it will close while checking.
(PHP 5 >= 5.5.0, PHP 7)
Generator::valid — 检查迭代器是否被关闭
此函数没有参数。
如果迭代器已被关闭返回 FALSE，否则返回 TRUE。
Notice if you call it with open empty generator, it will close while checking.