mysqli - Close connection in php using database class -

i have created database class in php, , want oop style not procedural style. here code when try close me error. function causing problem.

class mysqldatabase {     private $connection;     public $message;      /**      * mysqldatabase constructor.      */     public function __construct()     {         $this->open_connection();     }      //object oriented style     public function open_connection()     {         // constant comes form config         $this->connection = new mysqli(db_server, db_user, db_pass, db_name);         /*          * "official" oo way it,          */          if ($this->connection->connect_error) {             die('connect error (' . mysqli_connect_errno() . ') ' . mysqli_connect_error());         } else {             $this->message = "success... " . $this->connection->host_info;         }     }      public function close_connection(){         if (isset($this->connection)) {             mysqli_close($this->connection);             unset($this->connection);         }     } } 

public function close_connection()     {         if(isset($this->connection))         {             $this->connection->close();             unset($this->connection);         }     }