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std::experi...conjunction(3) C++ Standard Libary std::experi...conjunction(3) NAME std::experimental::conjunction - std::experimental::conjunction Synopsis Defined in header <experimental/type_traits> template<class... B> (library fundamentals TS v2) struct conjunction; Forms the logical conjunction of the type traits B..., effectively performing a logical AND on the sequence of traits. The specialization std::experimental::conjunction<B1, ..., BN> has a public and unambiguous base that is * if sizeof...(B) == 0, std::true_type; otherwise * the first type Bi in B1, ..., BN for which bool(Bi::value) == false, or BN if there is no such type. The member names of the base class, other than conjunction and oper- ator=, are not hidden and are unambiguously available in conjunction. Conjunction is short-circuiting: if there is a template type argu- ment Bi with bool(Bi::value) == false, then instantiating conjunction<B1, ..., BN>::value does not require the instantiation of Bj::value for j > i. Template parameters B... - every template argument Bi for which Bi::value is instanti- ated must be usable as a base class and define member value that is convertible to bool Helper variable template template<class... B> constexpr bool conjunction_v = (library fundamentals TS v2) conjunction<B...>::value; Possible implementation template<class...> struct conjunction : std::true_type { }; template<class B1> struct conjunction<B1> : B1 { }; template<class B1, class... Bn> struct conjunction<B1, Bn...> : std::conditional_t<bool(B1::value), conjunction<Bn...>, B1> {}; Notes A specialization of conjunction does not necessarily inherit from either std::true_type or std::false_type: it simply inherits from the first B whose ::value, converted to bool, is false, or from the very last B when all of them convert to true. For example, conjunction<std::integral_con- stant<int, 2>, std::integral_constant<int, 4>>::value is 4. Example // Run this code // func is enabled if all Ts... have the same type template<typename T, typename... Ts> std::enable_if_t<std::experimental::conjunction_v<std::is_same<T, Ts>...> > func(T, Ts...) { // TODO something to show } See also conjunction variadic logical AND metafunction (C++17) (class template) http://cppreference.com 2022.07.31 std::experi...conjunction(3)
NAME | Synopsis | Template parameters | Possible implementation | Notes | Example | See also
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