C++

28.9    “variant” for One of Several Types

With this template, you can model something similar to a union, but in a safer form.

A union has the problem in safe programming that constructors or destructors of the contained objects are not reliably called.

A variant can take the value of one of several types. Setting a value of one type changes the state of variant, so attempting to read another type from it then fails. Thus, its usage is safe.

// https://godbolt.org/z/baY7Tz91f#include <variant>using std::get;int main() {    std::variant<int, float> v{};    v = 12;                   // State changes to int    auto i = get<int>(v);     // retrieves the int    std::cout << i << '\n';   // Output: 12    v = 3.456f;               // State changes to float    std::cout << get<float>(v) << '\n';  // Output: ...