No offense but that's a wrong take on sum types. Sum types should be baked in the same way basic POD structs are, they're that fundamental. That D still doesn't

No offense but that's a wrong take on sum types. Sum types should be baked in the same way basic POD structs are, they're that fundamental. That D still doesn't have them as a core construct (along with pattern matching as the core mechanism to inspect the values) is, to me, a weakness inherited from C++ and other 1990s OO-driven languages, and patched in the same insufficient way (see std::variant).