mysql - PHP destruct function show an error? -

i have error shown in destruct function in class connects data base, tried remove variable in destruct function shows error. here code:

class db_connect {     function __construct() {         $this->connect();         echo "connected succesfully";     }     function __destruct() {         $this->close();     }      function connect() {         require_once __dir__ . '/db_config.php';          $con = mysqli_connect(db_server, db_user, db_password, db_database)                  or die(mysqli_error());         if($con){             echo "connected succesfully";         }         return $con;     }      function close() {         mysqli_close($con);     } } 

and there error message:

mysqli_close() expects parameter 1 mysqli

in connect method not assigning mysqli object instance variable.

in __destruct $con undefined/null explains error message.

require_once __dir__ . '/db_config.php';  class db_connect {     private $conn;     function __construct() {         $this->connect();     }      function __destruct() {         $this->close();     }      function connect() {         $this->conn = mysqli_connect(db_server, db_user, db_password, db_database)                            or die(mysqli_error());         echo "connected succesfully";     }      function close() {         mysqli_close($this->conn);     } }