fixes #389 #to_csv: changed predefined arguments and add documentation

README.md

@@ -156,6 +156,19 @@ sheet.to_xml
 sheet.to_yaml
 ```
 
+You can specified file as default argument to `#to_csv`: 
+
+```ruby
+# puts csv format content into a specified file
+sheet.to_csv(File.new("/dev/null"))
+```
+
+also you can specify the custom separator for the content:
+
+```ruby
+sheet.to_csv(separator: ":") # "," is used by default
+```
+
 ### Excel (xlsx and xlsm) Support
 
 Stream rows from an Excelx spreadsheet.

lib/roo/formatters/csv.rb

@@ -1,7 +1,7 @@
 module Roo
   module Formatters
     module CSV
-      def to_csv(filename = nil, separator = ",", sheet = default_sheet)
+      def to_csv(filename = nil, separator: ",", sheet: default_sheet)
         if filename
           File.open(filename, "w") do |file|
             write_csv_content(file, sheet, separator)

spec/lib/roo/base_spec.rb

@@ -269,7 +269,7 @@ def sheets
     end
 
     it 'should convert the spreadsheet to csv using the separator when is passed on the parameter' do
-      expect(spreadsheet.to_csv(nil, ';')).to eq(expected_csv_with_semicolons)
+      expect(spreadsheet.to_csv(separator: ';')).to eq(expected_csv_with_semicolons)
     end
   end
 end