28   auto& result = arg;  variable
29   if (!result.ok()) {
31                      << result.error().Trace();
38   auto& result = arg;  variable
39   if (result.ok()) {
47   auto& result = arg;  variable
48   using ResultType = std::decay_t<decltype(result)>;
52       result, result_listener);
56   auto& result = arg;  variable
57   using ResultType = std::decay_t<decltype(result)>;
64       result, result_listener);