Replacing legacy C-style tagged unions with std::variant in Modern C++:

using Command = std::variant<PingCmd, AuthCmd, DataCmd>;

void ExecuteCommand(const Command& cmd) {
    std::visit([](const auto& c) {
        c.Run();
    }, cmd);
}

std::variant guarantees that non-trivial constructors and destructors of held types are properly invoked on reassignment, completely eliminating memory corruption bugs common in raw C union types.

Combining std::visit with an overloaded lambda pattern (template<class... Ts> struct overloaded : Ts...;) gives C++ Haskell-style pattern matching!

Type safety with zero heap allocation: variant stores the payload inline inside its own memory layout with a 1-byte type index.