std::variant_alternative, std::variant_alternative_t
From cppreference.com
| Defined in header <variant>
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| template <std::size_t I, class T> struct variant_alternative; /* undefined */ |
(1) | (since C++17) |
| template <size_t I, class... Types> struct variant_alternative<I, variant<Types...>>; |
(2) | (since C++17) |
| template <size_t I, class T> class variant_alternative<I, const T>; template <size_t I, class T> class variant_alternative<I, volatile T>; |
(3) | (since C++17) |
Provides compile-time indexed access to the types of the alternatives of the possibly cv-qualified variant, combining cv-qualifications of the variant (if any) with the cv-qualifications of the alternative.
Formally,
2) meets the
TransformationTrait requirements with a member typedef type equal to the type of the alternative with index I3) meets the
TransformationTrait requirements with a member typedef type that names, respectively, std::add_const_t<std::variant_alternative<I,T>>, std::add_volatile_t<std::variant_alternative<I,T>>, and std::add_cv_t<std::variant_alternative<I,T>>Contents |
[edit] Member types
| Member type | Definition |
| type | the type of Ith alternative of the variant, where I must be in [0, sizeof...(Types)), otherwise the behavior is undefined
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[edit] Helper template alias
| template <size_t I, class T> using variant_alternative_t = typename variant_alternative<I, T>::type; |
(since C++17) | |
[edit] Example
| This section is incomplete Reason: no example |
[edit] See also
| (C++17) |
obtains the size of the variant's list of alternatives at compile time (class template) (variable template) |
| obtains the type of the specified element (class template specialization) |