std::variant<int, float, std::string> v = "hello"; std::visit([](auto&& arg) std::cout << arg; , v); Type-erased container for any copyable type.
std::vector<int> v(1'000'000); std::for_each(std::execution::par, v.begin(), v.end(), [](int& x) x *= 2; ); Portable filesystem operations: paths, directories, permissions, etc. c++ 2017
Type-safe union.
template<typename... Args> auto sum(Args... args) return (args + ...); // right fold v = "hello"