C++14. Declare a function with same-type-and-fixed-length argument list

Question

Is there a possible way to implement sort of helper struct using C++14 which takes as a template argument a Number, return type Ret and input type T and would contain a member type std::function<Ret(T...)> where sizeof...(T) == Number?

Answer 1

I suppose the following C++14 code can show you a way

#include <utility>
#include <functional>
#include <type_traits>

template <typename T, std::size_t>
using use_type = T;

template <typename...>
struct bar;

template <typename Ret, typename T, std::size_t ... Is>
struct bar<Ret, T, std::index_sequence<Is...>>
 { std::function<Ret(use_type<T, Is>...)> func; };

template <std::size_t N, typename Ret, typename T>
struct foo : public bar<Ret, T, std::make_index_sequence<N>>
 { };

int main ()
 {
   using T1 = std::function<void(int, int, int)>;
   using T2 = decltype(foo<3u, void, int>::func);

   static_assert( std::is_same<T1, T2>::value, "!" );
 }