std::variant_size, std::variant_size_v
Defined in header <variant>
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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>>
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
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type
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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
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) |