Parse error: syntax error, unexpected '$this' (T_VARIABLE) in F:\0000000000000\php\curl\vendor\jshensh\php-curl-class\src\Multi.php on line 38: ``` private function getChGenerator() { yield from $this->clientArr; //这一句在php5.6.27下有问题吗?看不出来 } ``` 如何解决呢?