intializing a std::array of objects that don't have default constructor from another constexpr std::array

Question

Is it possible to initialize an array of objects whose members are initialized from another constexpr array of trivial objects. For example I have the following

struct X
{
  X(int y): _x(y){}
  int _x;
};

struct Z
{
  static constexpr std::array<int, 4> arr = {1,6,0,4};
  

  // How does one implement make_array below that constructs
  // X[0] from arr[0], X[1] from arr[1], etc.
  // Is it even feasible in C++14/17?
  std::array<X, arr.size()> xArr = make_array(  );  

};

Answer 1

With std::index_sequence:

template <typename T, typename U, std::size_t N, std::size_t ... Is>
constexpr std::array<T, N> make_array(const std::array<U, N>& a, std::index_sequence<Is...>)
{
    return {{T(a[Is])...}};
}

template <typename T, typename U, std::size_t N>
constexpr std::array<T, N> make_array(const std::array<U, N>& a)
{
    return make_array<T>(a, std::make_index_sequence<N>());
}

Usage:

static constexpr std::array<int, 4> arr = {1,6,0,4};
  
/*constexpr*/ std::array<X, arr.size()> xArr = make_array<X>(arr);  

Demo