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

I suppose this is exactly what you asked for:

#include 
#include 

constexpr int N{4};
constexpr std::array shape {{1,3,5,2}};

// Diagnositcs

template
struct TPrintf {
        constexpr static void call(V v, Vals ...vals) {
                std::cout << v << " ";
                TPrintf::call(vals...);
        }
};

template
struct TPrintf {
        constexpr static void call(V v) {
                std::cout << v << std::endl;
        }
};


template
constexpr void t_printf(Vals ...vals) {
        TPrintf::call(vals...);
}

// Unroll

template
struct NestedLoops {
        template
        constexpr static void call(const F& f, RtIdx ...idx) {
                for(int i = 0; i < shape[CtIdx]; ++i) {
                        NestedLoops::call(f, idx..., i);
                }
        }
};

template
struct NestedLoops {
        template
        constexpr static void call(const F& f, RtIdx ...idx) {
                for(int i = 0; i < shape[N-1]; ++i) {
                        f(idx..., i);
                }
        }
};

template
void nested_loops(const F& f) {
        NestedLoops<0, F>::call(f);
}

int main()
{
        auto lf = [](int i, int j, int k, int l) {
                t_printf(i,j,k,l);
        };

        nested_loops(lf);
        return 0;
}