Use #tr instead of #gsub where possible

actionview/lib/action_view/helpers/form_tag_helper.rb

@@ -862,7 +862,7 @@ module ActionView
 
         # see http://www.w3.org/TR/html4/types.html#type-name
         def sanitize_to_id(name)
-          name.to_s.delete(']').gsub(/[^-a-zA-Z0-9:.]/, "_")
+          name.to_s.delete(']').tr('^-a-zA-Z0-9:.', "_")
         end
     end
   end

actionview/lib/action_view/template.rb

@@ -321,7 +321,7 @@ module ActionView
       end
 
       def identifier_method_name #:nodoc:
-        inspect.gsub(/[^a-z_]/, '_')
+        inspect.tr('^a-z_', '_')
       end
 
       def instrument(action, &block)