std::experimental::make_array
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Library fundamentals v2
experimental::make_array
Defined in header
<experimental/array>
template< class D = void, class... Types >
constexpr std::array <VT /* see below */, sizeof...(Types)> make_array( Types&&... t );
(library fundamentals TS v2)
constexpr std::array <VT /* see below */, sizeof...(Types)> make_array( Types&&... t );
Creates a std::array whose size is equal to the number of arguments and whose elements are initialized from the corresponding arguments. Returns std::array <VT, sizeof...(Types)>{std::forward <Types>(t)...}.
If D is void, then the deduced type VT is std::common_type_t <Types...>. Otherwise, it is D.
If D is void and any of std::decay_t <Types>... is a specialization of std::reference_wrapper , the program is ill-formed.
[edit] Notes
make_array is removed in Library Fundamentals TS v3 because the deduction guide for std::array and std::to_array have been already in C++20.
[edit] Possible implementation
namespace details { template<class> struct is_ref_wrapper : std::false_type {}; template<class T> struct is_ref_wrapper<std::reference_wrapper <T>> : std::true_type {}; template<class T> using not_ref_wrapper = std::negation <is_ref_wrapper<std::decay_t <T>>>; template<class D, class...> struct return_type_helper { using type = D; }; template<class... Types> struct return_type_helper<void, Types...> : std::common_type <Types...> { static_assert(std::conjunction_v <not_ref_wrapper<Types>...>, "Types cannot contain reference_wrappers when D is void"); }; template<class D, class... Types> using return_type = std::array <typename return_type_helper<D, Types...>::type, sizeof...(Types)>; } template<class D = void, class... Types> constexpr details::return_type<D, Types...> make_array(Types&&... t) { return {std::forward <Types>(t)...}; }
[edit] Example
Run this code
#include <experimental/array> #include <iostream> #include <type_traits> int main() { auto arr = std::experimental::make_array(1, 2, 3, 4, 5); bool is_array_of_5_ints = std::is_same <decltype(arr), std::array <int, 5>>::value; std::cout << "Returns an array of five ints? "; std::cout << std::boolalpha << is_array_of_5_ints << '\n'; }
Output:
Returns an array of five ints? true
[edit] See also
C++ documentation for
std::array deduction guides