def change_row_font(row_index, change_type, arg, font)
      validate_workbook
      ensure_cell_exists(row_index)

      xf = workbook.register_new_font(font, get_row_xf(row_index))
      row = sheet_data[row_index]
      row.style_index = workbook.register_new_xf(xf)
      row.cells.each { |c| c.font_switch(change_type, arg) unless c.nil? }
    end
def change_row_font(row_index, change_type, arg, font)
      validate_workbook
      ensure_cell_exists(row_index)

      xf = workbook.register_new_font(font, get_row_xf(row_index))
      row = sheet_data[row_index]
      row.style_index = workbook.register_new_xf(xf)
      row.cells.each { |c| c.font_switch(change_type, arg) unless c.nil? }
    end
Helper method to update the row styles array
 change_type - NAME or SIZE or COLOR etc
 main method to change font, called from each separate font mutator method