Genuine question, how would error set unioning work with payloads? error.WriterFailed (might be getting the exact name wrong) is returned from many different writers, whether writing to a statically allocated array, writing to a socket, or writing to a file. Each error would have a very different payload, so how would you disambiguate between the different payloads with a global error type? The way I see it is either you have error sets, or payloads, but not both.