C++: What is std::variant and std::optional?

1std::optional<int> find(int key) {
2    if (auto it = map.find(key); it != map.end())
3        return it->second;
4    return std::nullopt;
5}
6
7if (auto val = find(42)) {
8    std::cout << *val;
9}

1std::variant<int, std::string, double> v = "hello";
2
3// std::get
4std::string s = std::get<std::string>(v);
5
6// std::visit
7std::visit([](auto&& arg) {
8    std::cout << arg;
9}, v);