error_reporting(E_ALL | E_STRICT);

    function &getVal() {
       $data = [];

       return $data['hey'];
       //return $whatever; 
    }

    function getVal2() {
       $data = [];

       return $data['hey'];
    }

    var_dump(getVal());  // No E_NOTICE error is issued - why?
    var_dump(getVal2()); // E_NOTICE error is issued.

问题是：为什么第一次调用中没有E_NOTICE错误？解释很可能是创建变量$data [‘hey’]来返回引用.但是,当$data [‘hey’](或$whatever,…)未定义时,发出E_NOTICE错误仍然是错误的.