std::variant_size, std::variant_size_v
From cppreference.com
| Defined in header <variant>
|
||
| template <class T> struct variant_size; /* undefined */ |
(1) | (since C++17) |
| template <class... Types> struct variant_size<std::variant<Types...>> |
(2) | (since C++17) |
| template <class T> class variant_size<const T>; template <class T> class variant_size<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,
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>>Contents |
[edit] Helper variable template
| template <class T> inline constexpr std::size_t variant_size_v = std::variant_size<T>::value; |
(since C++17) | |
Inherited from std::integral_constant
Member constants
| value [static] |
sizeof...(Types) (public static member constant) |
Member functions
| operator std::size_t |
converts the object to std::size_t, returns value (public member function) |
| operator() (C++14) |
returns value (public member function) |
Member types
| Type | Definition |
value_type
|
std::size_t
|
type
|
std::integral_constant<std::size_t, value> |
[edit] Notes
All specializations of std::variant_size satisfy UnaryTypeTrait with BaseCharacteristic std::integral_constant<std::size_t, N> for some N.
[edit] Example
| This section is incomplete Reason: no example |
[edit] See also
| 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) |