std::experimental::make_array
From cppreference.com
< cpp | experimental
| Defined in header <experimental/array>
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| template< class D = void, class... Types > constexpr std::array<VT /* see below */, sizeof...(Types)> make_array( Types&&... t ); |
(library fundamentals TS v2) | |
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.
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.
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)...}; } |
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
See also
| C++ documentation for
std::array deduction guides | |
| creates a std::array object from a built-in array (function template) | |