std::variant_size, std::variant_size_v - cppreference.com (original) (raw)
| Defined in header | ||
|---|---|---|
| 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>; | (3) | (since C++17) |
| template< class T > class variant_size<volatile T>; | (4) | (since C++17) (deprecated in C++20) |
| template< class T > class variant_size<const volatile T>; | (5) | (since C++17) (deprecated in C++20) |
Provides access to the number of alternatives in a possibly cv-qualified variant as a compile-time constant expression.
Formally,
Contents
[edit] Helper variable template
| template< class T > constexpr std::size_t variant_size_v = std::variant_size<T>::value; | | (since C++17) | | --------------------------------------------------------------------------------------------------------------------------- | | ------------- |
Inherited from std::integral_constant
Member constants
| | sizeof...(Types) (public static member constant) | | --------------------------------------------------- |
Member functions
| | converts the object to std::size_t, returns value (public member function) | | ----------------------------------------------------------------------------------------------------------- | | | returns value (public member function) |
Member types
[edit] Notes
All specializations of std::variant_size satisfy UnaryTypeTrait with base characteristic std::integral_constant<std::size_t, N> for some N.