C++: What is std::variant in C++17?

1#include <variant>
2#include <string>
3
4std::variant<int, double, std::string> v;
5
6v = 42;           // int
7v = 3.14;         // double
8v = "hello";      // string
9
10// Access
11std::cout << std::get<int>(v);        // 42
12std::cout << std::get<2>(v);          // string
13std::cout << std::get<std::string>(v); // hello
14
15// Safe access
16if (auto* p = std::get_if<int>(&v)) {
17    std::cout << *p;
18}
19
20// Visit
21std::visit([](auto&& arg) {
22    std::cout << arg << "\n";
23}, v);