public function lastColumn()
    {
        $xlSheet = $this->xlSheet();
        $highestColumn = $xlSheet->getHighestColumn(); // e.g 'F'
        $highestColumnIndex = Cell\Coordinate::columnIndexFromString($highestColumn); // e.g. 5

        return $highestColumnIndex;
    }
public function lastColumn()
    {
        $xlSheet = $this->xlSheet();
        $highestColumn = $xlSheet->getHighestColumn(); // e.g 'F'
        $highestColumnIndex = Cell\Coordinate::columnIndexFromString($highestColumn); // e.g. 5

        return $highestColumnIndex;
    }
{@inheritDoc}
@link https://phpspreadsheet.readthedocs.io/en/develop/topics/accessing-cells/#looping-through-cells-using-indexes