I agree, you really want a sum, not a tuple - that's why my example was absl::StatusOr<T>, not std::pair. But a tuple plus tooling support (e.g., linters in Go

I agree, you really want a sum, not a tuple - that's why my example was absl::StatusOr<T>, not std::pair. But a tuple plus tooling support (e.g., linters in Go that don't allow you to not use the returned error value) can emulate a sum type.