std::experimental::make_array (3) - Linux Manuals

std::experimental::make_array: std::experimental::make_array

NAME

std::experimental::make_array - std::experimental::make_array

Synopsis

Defined in header <experimental/array>
template <class D = void, class... Types> (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.

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()
  {
      decltype(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