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#pragma once
#include <util/generic/store_policy.h>
#include <tuple>
namespace NPrivate {
template <typename... TContainers>
struct TCartesianMultiplier {
template <std::size_t... I>
struct TCartesianMultiplierWithIndex {
private:
using THolders = std::tuple<TAutoEmbedOrPtrPolicy<TContainers>...>;
using TValue = std::tuple<decltype(*std::begin(std::declval<TContainers&>()))...>;
using TIteratorState = std::tuple<int, decltype(std::begin(std::declval<TContainers&>()))...>;
using TSentinelState = std::tuple<int, decltype(std::end(std::declval<TContainers&>()))...>;
struct TIterator;
struct TSentinelCandidate {
TSentinelState Iterators_;
THolders* HoldersPtr_;
};
using TSentinel = std::conditional_t<std::is_same_v<TIteratorState, TSentinelState>,
TIterator, TSentinelCandidate>;
struct TIterator {
private:
//! Return value is true when iteration is not finished
template <std::size_t position = sizeof...(TContainers)>
void IncrementIteratorsTuple() {
auto& currentIterator = std::get<position>(Iterators_);
++currentIterator;
if (currentIterator != std::end(*std::get<position - 1>(*HoldersPtr_).Ptr())) {
return;
} else {
currentIterator = std::begin(*std::get<position - 1>(*HoldersPtr_).Ptr());
if constexpr (position != 1) {
IncrementIteratorsTuple<position - 1>();
} else {
std::get<0>(Iterators_) = 1;
}
}
}
public:
using difference_type = std::ptrdiff_t;
using value_type = TValue;
using pointer = TValue*;
using reference = TValue&;
using iterator_category = std::input_iterator_tag;
TValue operator*() {
return {*std::get<I + 1>(Iterators_)...};
}
TValue operator*() const {
return {*std::get<I + 1>(Iterators_)...};
}
void operator++() {
IncrementIteratorsTuple();
}
bool operator!=(const TSentinel& other) const {
// not finished iterator VS sentinel (most frequent case)
if (std::get<0>(Iterators_) != std::get<0>(other.Iterators_)) {
return true;
}
// do not compare sentinels and finished iterators
if (std::get<0>(other.Iterators_)) {
return false;
}
// compare not finished iterators
return ((std::get<I + 1>(Iterators_) != std::get<I + 1>(other.Iterators_)) || ...);
}
bool operator==(const TSentinel& other) const {
return !(*this != other);
}
TIteratorState Iterators_;
THolders* HoldersPtr_;
};
public:
using iterator = TIterator;
using const_iterator = TIterator;
using value_type = typename TIterator::value_type;
using reference = typename TIterator::reference;
using const_reference = typename TIterator::reference;
TIterator begin() const {
bool isEmpty = !((std::begin(*std::get<I>(Holders_).Ptr()) != std::end(*std::get<I>(Holders_).Ptr())) && ...);
return {TIteratorState{int(isEmpty), std::begin(*std::get<I>(Holders_).Ptr())...}, &Holders_};
}
TSentinel end() const {
return {TSentinelState{1, std::end(*std::get<I>(Holders_).Ptr())...}, &Holders_};
}
mutable THolders Holders_;
};
template <std::size_t... I>
static auto CartesianMultiply(TContainers&&... containers, std::index_sequence<I...>) {
return TCartesianMultiplierWithIndex<I...>{{std::forward<TContainers>(containers)...}};
}
};
}
//! Usage: for (auto [ai, bi] : CartesianProduct(a, b)) {...}
//! Equivalent: for (auto& ai : a) { for (auto& bi : b) {...} }
template <typename... TContainers>
auto CartesianProduct(TContainers&&... containers) {
return NPrivate::TCartesianMultiplier<TContainers...>::CartesianMultiply(
std::forward<TContainers>(containers)..., std::make_index_sequence<sizeof...(TContainers)>{});
}
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