How to generate nested loops at compile time

Question

I have an integer N which I know at compile time. I also have an std::array holding integers describing the shape of an N-dime

Answer 1

Something like this (NOTE: I take the "shape" as a variadic template argument set..)

#include 

template 
struct Looper{
    template 
    constexpr void operator()(F& f, X... x) {
        for (int i = 0; i < I; ++i) {
            Looper()(f, x..., i);
        }
    }
};

template 
struct Looper{
    template 
    constexpr void operator()(F& f, X... x) {
        for (int i = 0; i < I; ++i) {
            f(x..., i);
        }
    }
};

int main()
{
    int v = 0;
    auto f = [&](int i, int j, int k, int l) {
        v += i + j + k + l;
    };

    Looper<1, 3, 5, 2>()(f);

    auto g = [&](int i) {
        v += i;
    };

    Looper<5>()(g);

    std::cout << v << std::endl;
}