Convert std::tuple to std::array C++11

Question

If I have std::tuple (where the type is homogeneous), is there a stock function or constructor to convert to std::array

Answer 1

Converting a tuple to an array without making use of recursion, including use of perfect-forwarding (useful for move-only types):

#include 
#include 
#include 

template
struct indices {
    using next = indices;
};

template
struct build_indices {
    using type = typename build_indices::type::next;
};

template<>
struct build_indices<0> {
    using type = indices<>;
};

template
using Bare = typename std::remove_cv::type>::type;

template
constexpr
typename build_indices>::value>::type
make_indices()
{ return {}; }

template
std::array<
  typename std::tuple_element<0, Bare>::type,
    std::tuple_size>::value
>
to_array(Tuple&& tuple, indices)
{
    using std::get;
    return {{ get(std::forward(tuple))... }};
}

template
auto to_array(Tuple&& tuple)
-> decltype( to_array(std::declval(), make_indices()) )
{
    return to_array(std::forward(tuple), make_indices());
}

int main() {
  std::tuple tup(1.5, 2.5, 4.5);
  auto arr = to_array(tup);
  for (double x : arr)
    std::cout << x << " ";
  std::cout << std::endl;
  return 0;
}