//单例模式class sigle{    private static $ins = null;        public static function getIns(){        if(self::$ins === null){            self::$ins = new self();        }                return self::$ins;    }        //方法签加final,则方法不能被覆盖，类前加final,则类不能被继承    final protected function __construct(){}    final protected function __clone(){}}$s1 = sigle::getIns();$s2 = sigle::getIns();if($s1 == $s2){    echo '是一个对象';}else{    echo '不是一个对象';}