Struct variant_size

Auxilia os objetos variantes.

Sintaxe

template <class T>
    struct variant_size; // not defined
template <class T>
    struct variant_size<const T>;
template <class T>
    struct variant_size<volatile T>;
template <class T>
    struct variant_size<const volatile T>;
template <class T>
    inline constexpr size_t variant_size_v = variant_size<T>::value;
template <class... Types>
    struct variant_size<variant<Types...>>;