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#pragma once
#include <util/generic/store_policy.h>
#include <limits>
#include <tuple>
namespace NPrivate {
template <typename TContainer>
struct TEnumerator {
private:
using TStorage = TAutoEmbedOrPtrPolicy<TContainer>;
using TValue = std::tuple<const std::size_t, decltype(*std::begin(std::declval<TContainer&>()))>;
using TIteratorState = decltype(std::begin(std::declval<TContainer&>()));
using TSentinelState = decltype(std::end(std::declval<TContainer&>()));
static constexpr bool TrivialSentinel = std::is_same_v<TIteratorState, TSentinelState>;
struct TIterator;
struct TSentinelCandidate {
TSentinelState Iterator_;
};
using TSentinel = std::conditional_t<TrivialSentinel, TIterator, TSentinelCandidate>;
struct TIterator {
using difference_type = std::ptrdiff_t;
using value_type = TValue;
using pointer = void;
using reference = value_type;
using iterator_category = std::input_iterator_tag;
reference operator*() const {
return {Index_, *Iterator_};
}
TIterator& operator++() {
++Index_;
++Iterator_;
return *this;
}
TIterator operator++(int) {
TIterator result = *this;
++(*this);
return result;
}
bool operator!=(const TSentinel& other) const {
return Iterator_ != other.Iterator_;
}
bool operator==(const TSentinel& other) const {
return Iterator_ == other.Iterator_;
}
std::size_t Index_;
TIteratorState Iterator_;
};
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 {
return {0, std::begin(*Storage_.Ptr())};
}
TSentinel end() const {
if constexpr (TrivialSentinel) {
return TIterator{std::numeric_limits<std::size_t>::max(), std::end(*Storage_.Ptr())};
} else {
return TSentinel{std::end(*Storage_.Ptr())};
}
}
mutable TStorage Storage_;
};
}
//! Usage: for (auto [i, x] : Enumerate(container)) {...}
template <typename TContainerOrRef>
auto Enumerate(TContainerOrRef&& container) {
return NPrivate::TEnumerator<TContainerOrRef>{std::forward<TContainerOrRef>(container)};
}
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