"Invalid" is different than "unknown but safely be round-trippable" though. We round-trip unknown-to-the-local-unmarshaller enums through our protobuf services or DB layers all the time.
If you want to carry marshaled data around without knowing what is, carry the marshaled data around. If you want to know what that data is and deal with it, marshal it into a known swift enum.
I honestly think we’re talking about different things… the guarantees a programming language gives you are independent of the guarantees a serialization format gives you.
