[jlouis]

Not a niche feature. Fundamental for any decent language with a type system.

[mistrial9]

ok, but C99 and C++11 and others, all have ways to implement types. "Fundemental" as you say.. using UNION in C++ is not a good choice to implement types.. in old C99, you can use UNION that way but why? footguns all around.

[saagarjha]

std::variant does not exist in C99.