Create static array with variadic templates

Question

There was an answer on stackoverflow (which I can\'t seem to find anymore) which demonstrated how a variadic template can be used in C++11 to create a static array at compil

Answer 1

In C++11 (and especially in C++14), the best way to initialize objects at compile-time is with constexpr constructors, not by playing metagames with the typesystem.

struct MyObject {
    int x_, y_;
    constexpr MyObject(int x, int y) : x_(x), y_(y) { }
};

const MyObject array[] = { MyObject(1,2), MyObject(3,4) };

You can apply your "generator function" idea here, too, if you really want to:

#include 

#if __cplusplus < 201400
template struct integer_sequence { typedef integer_sequence type; };
template struct make_index_sequence;
template struct make_index_sequence<0, II...> : integer_sequence {};
template struct make_index_sequence : make_index_sequence {};
#define HACK(x) typename x::type
#else
#include   // the C++14 way of doing things
using std::integer_sequence;
using std::make_index_sequence;
#define HACK(x) x
#endif


struct MyObject {
    int x_, y_;
    constexpr MyObject(int x, int y) : x_(x), y_(y) { }
};

template
struct GeneratedArrayHelper;

template
struct GeneratedArrayHelper> {
    static const T data[N];  // element i is initialized with Func(i)
};

template
const T GeneratedArrayHelper>::data[N] =
    { Func(i)... };

template
struct GeneratedArray :
    GeneratedArrayHelper)> {};

constexpr MyObject newObject(int i) { return MyObject(2*i, 2*i+1); }

int main() {
    for (const MyObject& m : GeneratedArray::data) {
        printf("%d %d\n", m.x_, m.y_);
    }

    // Output:
    //   0 1
    //   2 3
    //   4 5
    //   6 7
    //   8 9
}

I don't know why Clang 3.5 and GCC 4.8 insist that I put the HACK() macro in there, but they refuse to compile the code without it. Probably I made some dumb mistake and someone can point it out. Also, I'm not confident that all the consts and constexprs are in the best places.