Defined in header <variant> | ||
|---|---|---|
template <class T> struct variant_size; /* undefined */ | (1) | (since C++17) |
template <class... Types>
struct variant_size<std::variant<Types...>>
: std::integral_constant<std::size_t, sizeof...(Types)> { };
| (2) | (since C++17) |
template <class T> class variant_size<const T>; template <class T> class variant_size<volatile T>; template <class T> class variant_size<const volatile T>; | (3) | (since C++17) |
Provides access to the number of alternatives in a possibly cv-qualified variant as a compile-time constant expression.
Formally,
std::integral_constant<std::size_t, sizeof...(Types)>
std::integral_constant<std::size_t, variant_size<T>>
template <class T> inline constexpr std::size_t variant_size_v = std::variant_size<T>::value; | (since C++17) |
| value
[static] | sizeof...(Types) (public static member constant) |
| operator std::size_t | converts the object to std::size_t, returns value (public member function) |
| operator()
(C++14) | returns value (public member function) |
| Type | Definition |
|---|---|
value_type | std::size_t |
type | std::integral_constant<std::size_t, value> |
All specializations of std::variant_size satisfy UnaryTypeTrait with BaseCharacteristic std::integral_constant<std::size_t, N> for some N.
|
(C++17) | obtains the type of the alternative specified by its index, at compile time (class template) (alias template) |
obtains the size of tuple at compile time (class template specialization) |
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