[mFixman]

Is this the first type of sum-type option choosing statement present for C++ unions? I've been waiting for this feature since the year 1978.

Still, it's a wasted opportunity not to have a language-level overload to the `switch` statement that allows nice pattern matching. Even with std::is_within_lifetime C++ unions are prone to errors and hard to work with.

[sebtron]

Since C++17 there is std::variant

https://en.cppreference.com/w/cpp/utility/variant.html

[maleldil]

These are not proper sum types, since you're limited to one variant per type.