build_expiry

# File actionpack/lib/action_controller/routing/route_set.rb, line 292
      def build_expiry(options, recall)
        recall.inject({}) do |expiry, (key, recalled_value)|
          expiry[key] = (options.key?(key) && options[key].to_param != recalled_value.to_param)
          expiry
        end
      end