Also cache row_ref

The `row_ref` method is called once for each column in a row and once at the
row level.

2 files changed, 3 insertions, 3 deletions

diff --git a/lib/axlsx.rb b/lib/axlsx.rb
index 30683458..bf16afbd 100644
--- a/lib/axlsx.rb
+++ b/lib/axlsx.rb
@@ -125,7 +125,6 @@ module Axlsx
       end
       chars.prepend((i + 65).chr)
       chars.freeze
-      chars
     end
   end
 
@@ -133,7 +132,8 @@ module Axlsx
   # @note The spreadsheet rows are 1-based and the passed in index is 0-based, so we add 1.
   # @return [String]
   def self.row_ref(index)
-    (index + 1).to_s
+    @row_ref ||= {}
+    @row_ref[index] ||= (index + 1).to_s.freeze
   end
 
   # @return [String] The alpha(column)numeric(row) reference for this sell.
diff --git a/lib/axlsx/workbook/worksheet/row.rb b/lib/axlsx/workbook/worksheet/row.rb
index 16116835..dc0320b7 100644
--- a/lib/axlsx/workbook/worksheet/row.rb
+++ b/lib/axlsx/workbook/worksheet/row.rb
@@ -89,7 +89,7 @@ module Axlsx
     # @param [String] str The string this rows xml will be appended to.
     # @return [String]
     def to_xml_string(r_index, str = +'')
-      serialized_tag('row', str, :r => r_index + 1) do
+      serialized_tag('row', str, :r => Axlsx.row_ref(r_index)) do
         each_with_index { |cell, c_index| cell.to_xml_string(r_index, c_index, str) }
       end
     end