My goal is to make this template work:
template <size_t... Ns>
struct mult
{
using cross = ?; // variadic size_t
static_assert(sizeof...(cross) + 1 == sizeof...(Ns), "");
};
So I can use it like this:
mult<2,3,5>::cross // 6,15 // because 2*3=6, 3*5=15
mult<3,5,7,11>::cross // 15,35,77 // because 3*5=15, 5*7=35, 7*11=77
Because I need to make this:
// tuple of arrays
std::tuple<std::array<size_t, mult<Ns...>::cross>...> cross_arrays;
If you want compile time computation, write constexpr functions
template<typename... SizeT>
constexpr auto cross(size_t x, SizeT... xs)
{
std::array tmp = {x, xs...};
std::array ret = {xs...};
for(size_t i = 0; i < ret.size(); i++)
ret[i] *= tmp[i];
return ret;
}
template<size_t... xs, size_t... Is>
auto cross_tuple_fn(std::index_sequence<Is...>)
{
constexpr auto dims = cross(xs...);
return std::tuple<std::array<size_t, dims[Is]>...>{};
}
template<size_t... xs>
auto cross_tuple_fn()
{
return cross_tuple_fn<xs...>(std::make_index_sequence<sizeof...(xs) - 1>{});
}
template<size_t... xs>
using cross_tuple_t = decltype(cross_tuple_fn<xs...>());
They're easier to read, write and looks more or less the same as normal functions.
Use as
cross_tuple_t<Ns...> cross_arrays;