std::variant_size,std::variant_size_v (3) - Linux Man Pages

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

NAME

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

See also


variant_alternative obtains the type of the alternative specified by its index, at compile time
variant_alternative_t (class template) (alias template)


(C++17)
                      obtains the size of tuple at compile time
tuple_size (class template specialization)