public static function call() { if (self::$db_instance == null) { self::$db_instance = new mysqli(HOST, USERNAME, PWD, DBNAME); if (self::$db_instance->connect_errno) { echo "Failed to connect to MySQL: (" . self::$db_instance->connect_errno . ") " . self::$db_instance->db_instance->connect_error; } } return self::$db_instance; }