php单例模式

<?phpclass single{private static $instance;// 设置成private为了防止直接newprivate function __construct(){echo 'this is construct'."<br>";}public static function getinstance(){if(!self::$instance instanceof self){self::$instance=new self;}return self::$instance;}public function __clone(){trigger_error('clone is not allow');// 为了防止克隆，也可以直接把此方法写成private}public function test(){echo 'test :do it';}}$a=new single();//Fatal error: Call to private single::__construct() fro// single::test();//ini_set('display_errors',0);// single::getinstance();$a=single::getinstance();$a->test();$clone = clone $a; // Notice: clone is not allow in