c++ constexpr and reference - c++

Question

Because of C++14 does not have constexpr array, I tried to create my own.
Here is the full code :
template<typename T, std::size_t N>
class constexpr_array {
public:
constexpr constexpr_array() = default;
template<typename U>
constexpr constexpr_array(std::initializer_list<U> values) :
m_array{} {
const U *it = values.begin();
for(std::size_t i{0}; i < N; ++i) {
m_array[i] = *it++;
}
}
constexpr constexpr_array(const constexpr_array&) = default;
constexpr constexpr_array(constexpr_array&&) = default;
constexpr T& operator[](std::size_t index) {
return m_array[index];
}
constexpr const T& operator[](std::size_t index) const {
return m_array[index];
}
constexpr const constexpr_array *operator&() const {
return this;
}
private:
T m_array[N];
};
It works well, however I wonder why it is not allowed, (maybe only by MSVC?) to have a initializer_list constructor like that :
template<typename U>
constexpr constexpr_array(std::initializer_list<U> values) :
m_array{} {
const U *it = values.begin();
for(auto &v : m_array) {
v = *it++;
}
}
I got c2131-expression-did-not-evaluate-to-a-constant in Visual Studio 2017. The error is at line for(auto &v : m_array).
Here is a sample to try :
template<std::size_t N, const constexpr_array<std::size_t, N> *indices>
struct array_to_index_sequence {
template<typename Indices = std::make_index_sequence<N>>
struct as_index_sequence{};
template<std::size_t ...Is>
struct as_index_sequence<std::index_sequence<Is...>> : std::index_sequence<(*indices)[Is]...>{};
};
template<int... I>
struct a {
static constexpr constexpr_array<std::size_t, 3> compute() {
return {I...};
}
static constexpr constexpr_array<std::size_t, 3> t = compute();
using i = typename array_to_index_sequence<3, &t>::template as_index_sequence<>;
};
#include <string>
template<std::size_t ...I>
void f(std::tuple<int, std::string, double, double> t, std::index_sequence<I...>) {
int a[] = {0, (std::cout << std::get<I>(t) << std::endl, 0)...};
}
int main()
{
f(std::make_tuple(5, "lolll", 1.0, 2.0), typename a<2, 1, 0>::i{});
return 0;
}