php单例模式

<?phpclass Db{static private $instance;static private $connectSource;private $dbConfig = array('host'=>'127.0.0.1','user'=>'root','password'=>'song123','databases'=>'zong',);private  function __construct(){}static public function getInstance(){if(!(self::$instance instanceof self)){self::$instance = new self();}return self::$instance;}     public function connect(){if(!self::$connectSource){self::$connectSource = mysqli_connect($this->dbConfig['host'],$this->dbConfig['user'],$this->dbConfig['password'],$this->dbConfig['databases']);if(!self::$connectSource){die('链接失败'.mysqli_error());}mysqli_select_db(self::$connectSource,$this->dbConfig['databases']);mysqli_query(self::$connectSource,'set names UTF8');}return self::$connectSource;}}// $a = Db::getInstance()->connect();// $sql = "select * from day1";// $result = mysqli_query($a,$sql);// var_dump($result);