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86 lines (75 loc) · 3.06 KB
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#include <tuple>
#include <iostream>
namespace detail {
template <typename...>
struct is_tuple : public std::false_type {};
template <typename ... Args>
struct is_tuple<std::tuple<Args...>> : public std::true_type {};
template <typename ... Args>
constexpr static bool is_tuple_v = is_tuple<Args...>::value;
template <typename Tuple, typename Func, size_t... Idx>
constexpr auto foreach_tuple(Tuple&& t, Func&& f, std::index_sequence<Idx...>) {
return (std::forward<Func>(f)(std::get<Idx>(std::forward<Tuple>(t)), Idx), ...);
}
template <size_t N, typename T, typename ... Args>
constexpr auto one_line_impl(const T& value, const std::tuple<Args...>& t) {
if constexpr (N + 1 == sizeof...(Args)) {
return std::make_tuple(value * std::get<N>(t));
}
else {
static_assert(std::is_integral_v<std::decay_t<T>> && std::is_integral_v<std::decay_t<std::tuple_element_t<N, std::tuple<Args...>>>>);
return std::tuple_cat(std::make_tuple(value * std::get<N>(t)), one_line_impl<N + 1>(value, t));
}
}
template <typename T, typename ... Args>
constexpr auto one_line(const T& left, const std::tuple<Args...>& t) {
static_assert(sizeof...(Args) > 0);
return one_line_impl<0>(left, t);
}
template <size_t N, typename ... Args1, typename ... Args2>
constexpr auto cartesian_impl(const std::tuple<Args1...>& t1, const std::tuple<Args2...>& t2) {
if constexpr ((N >= sizeof...(Args1))) {
return std::tuple<>{};
}
else {
return std::tuple_cat(std::make_tuple(one_line(std::get<N>(t1), t2)), cartesian_impl<N + 1>(t1, t2));
}
}
template <typename ... Args1, typename ... Args2>
constexpr auto cartesian(const std::tuple<Args1...>& t1, const std::tuple<Args2...>& t2) {
return detail::cartesian_impl<0>(t1, t2);
}
}
template <typename Tuple, typename Func>
constexpr auto foreach(Tuple&& t, Func&& f) {
using raw_tuple_type = std::decay_t<Tuple>;
if constexpr (detail::is_tuple_v<raw_tuple_type>) {
return detail::foreach_tuple(std::forward<Tuple>(t), std::forward<Func>(f), std::make_index_sequence<std::tuple_size_v<raw_tuple_type>>{});
}
else {
throw std::invalid_argument("only tuple");
}
}
template <typename ... Args1, typename ... Args2>
constexpr auto operator*(const std::tuple<Args1...>& t1, const std::tuple<Args2...>& t2) {
return detail::cartesian(t1, t2);
}
int main() {
const auto t1 = std::make_tuple(1, 2, 3);
const auto t2 = std::make_tuple(1, 2, 3);
const auto t = t1 * t2;
foreach(t, [](const auto& element, size_t idx) {
using tuple_type = std::decay_t<decltype(element)>;
std::cout << idx << std::endl;
foreach(element, [](const auto& sub, size_t index) { std::cout << sub << " "; });
std::cout << std::endl;
});
// output:
// 0
// 1 2 3
// 1
// 2 4 6
// 2
// 3 6 9
return 0;
}