Std::variant_size,std::variant_size_v (3) Linux Manual Page

std::variant_size,std::variant_size_v – std::variant_size,std::variant_size_v

Synopsis

Defined in header<variant>

    template <class T>
    (1)(since C++ 17)

        struct variant_size; /* undefined */

template <class... Types>

struct variant_size<std::variant<Types...>>(2)(since C++ 17)

    : std::integral_constant<std::size_t, sizeof...(Types)> {
};

template <class T>
class variant_size<const T>;

template <class T>
class variant_size<volatile T>;
(3)(since C++ 17)

    template <class T>
    class variant_size<const volatile T>;

Provides access to the number of alternatives in a possibly cv-qualified variant as a compile-time constant expression.
Formally,
2) meets the UnaryTypeTrait requirements with a BaseCharacteristic of std::integral_constant<std::size_t, sizeof…(Types)>
3) meets the UnaryTypeTrait requirements with a BaseCharacteristic of std::integral_constant<std::size_t, variant_size<T>>
Helper variable template

template <class T>                                                          (since C++17)

inline constexpr std::size_t variant_size_v = std::variant_size<T>::value;

Inherited from std::integral_constant

Member constants

value sizeof…(Types)
(public static member constant)
[static]

Member functions

converts the object to std::size_t, returns value
operator std::size_t (public member function)

operator() returns value
(public member function)
(C++14)

Member types

Type Definition
value_type std::size_t
type std::integral_constant<std::size_t, value>

Notes

All specializations of std::variant_size satisfy UnaryTypeTrait with BaseCharacteristic std::integral_constant<std::size_t, N> for some N.

Example

This section is incomplete
Reason: no example

std::variant_size,std::variant_size_v (3) Linux Manual Page