these variables are also private

actionpack/lib/abstract_controller/rendering.rb

@@ -58,6 +58,7 @@ def rendered_format
     DEFAULT_PROTECTED_INSTANCE_VARIABLES = %w(
       @_action_name @_response_body @_formats @_prefixes @_config
       @_view_context_class @_view_renderer @_lookup_context
+      @_routes @_db_runtime
     ).map(&:to_sym)
 
     # This method should return a hash with assigns.