public static function createWriter(Spreadsheet $spreadsheet, $writerType)
    {
        if (!isset(self::$writers[$writerType])) {
            throw new Writer\Exception("No writer found for type $writerType");
        }

        // Instantiate writer
        $className = self::$writers[$writerType];
        $writer = new $className($spreadsheet);

        return $writer;
    }