Create N-element constexpr array in C++11

Question

Hello i'm learning C++11, I'm wondering how to make a constexpr 0 to n array, for example:

n = 5;  int array[] = {0 ... n}; 

so array may be {0, 1, 2, 3, 4, 5}

Answer 1

In C++14 it can be easily done with a constexpr constructor and a loop:

#include <iostream>  template<int N> struct A {     constexpr A() : arr() {         for (auto i = 0; i != N; ++i)             arr[i] = i;      }     int arr[N]; };  int main() {     constexpr auto a = A<4>();     for (auto x : a.arr)         std::cout << x << '\n'; } 

Answer 2

Unlike those answers in the comments to your question, you can do this without compiler extensions.

#include <iostream>  template<int N, int... Rest> struct Array_impl {     static constexpr auto& value = Array_impl<N - 1, N, Rest...>::value; };  template<int... Rest> struct Array_impl<0, Rest...> {     static constexpr int value[] = { 0, Rest... }; };  template<int... Rest> constexpr int Array_impl<0, Rest...>::value[];  template<int N> struct Array {     static_assert(N >= 0, "N must be at least 0");      static constexpr auto& value = Array_impl<N>::value;      Array() = delete;     Array(const Array&) = delete;     Array(Array&&) = delete; };  int main() {     std::cout << Array<4>::value[3]; // prints 3 }