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

Assuming you don't want total loop unrolling, just generation of i, j, k etc. argument tuples for f:

#include 
#include       // std::integer_sequence

template< int dim >
constexpr auto item_size_at()
    -> int
{ return ::shape[dim + 1]*item_size_at(); }

template<> constexpr auto item_size_at<::N-1>() -> int { return 1; }

template< size_t... dim >
void call_f( int i, std::index_sequence )
{
    f( (i/item_size_at() % ::shape[dim])... );
}

auto main()
    -> int
{
    int const n_items = ::shape[0]*item_size_at<0>();
    for( int i = 0; i < n_items; ++i )
    {
        call_f( i, std::make_index_sequence<::N>() );
    }
}