I'm finding that wrapping an interface in a struct can be a good technique. However, the interface{} contains a type identifier, so adding another one seems like wasted space. Usually you can compute it using a type switch.
Yeah, that's a perfectly valid solution as well. Depending on the application it may be faster to do the assertion on your type identifier rather than introspecting the type though. And having a list of type options more directly maps to a true sum type. I probably wouldn't actually do it in real Go code if I could avoid it though
