// Originally taken from
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// https://github.com/cryfs/cryfs/blob/14ad22570ddacef22d5ff139cdff68a54fc8234d/src/cpp-utils/either.h
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#pragma once
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#include <c10/macros/Macros.h>
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#include <c10/util/C++17.h>
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#include <c10/util/Optional.h>
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#include <iostream>
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namespace c10 {
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/**
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* either<A, B> is a tagged union that holds either an object of type A
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* or an object of type B.
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*/
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template <class Left, class Right>
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class either final {
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public:
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template <
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class Head,
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class... Tail,
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c10::guts::enable_if_t<
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std::is_constructible<Left, Head, Tail...>::value &&
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!std::is_constructible<Right, Head, Tail...>::value>* = nullptr>
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either(Head&& construct_left_head_arg, Tail&&... construct_left_tail_args)
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: _side(Side::left) {
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_construct_left(
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std::forward<Head>(construct_left_head_arg),
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std::forward<Tail>(construct_left_tail_args)...);
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}
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template <
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class Head,
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class... Tail,
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c10::guts::enable_if_t<
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!std::is_constructible<Left, Head, Tail...>::value &&
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std::is_constructible<Right, Head, Tail...>::value>* = nullptr>
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either(Head&& construct_right_head_arg, Tail&&... construct_right_tail_args)
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: _side(Side::right) {
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_construct_right(
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std::forward<Head>(construct_right_head_arg),
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std::forward<Tail>(construct_right_tail_args)...);
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}
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either(const either<Left, Right>& rhs) : _side(rhs._side) {
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if (_side == Side::left) {
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_construct_left(
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rhs._left); // NOLINT(cppcoreguidelines-pro-type-union-access)
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} else {
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_construct_right(
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rhs._right); // NOLINT(cppcoreguidelines-pro-type-union-access)
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}
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}
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either(either<Left, Right>&& rhs) noexcept : _side(rhs._side) {
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if (_side == Side::left) {
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_construct_left(std::move(
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rhs._left)); // NOLINT(cppcoreguidelines-pro-type-union-access)
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} else {
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_construct_right(std::move(
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rhs._right)); // NOLINT(cppcoreguidelines-pro-type-union-access)
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}
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}
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~either() {
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_destruct();
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}
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either<Left, Right>& operator=(const either<Left, Right>& rhs) {
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_destruct();
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_side = rhs._side;
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if (_side == Side::left) {
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_construct_left(
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rhs._left); // NOLINT(cppcoreguidelines-pro-type-union-access)
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} else {
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_construct_right(
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rhs._right); // NOLINT(cppcoreguidelines-pro-type-union-access)
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}
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return *this;
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}
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either<Left, Right>& operator=(either<Left, Right>&& rhs) {
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_destruct();
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_side = rhs._side;
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if (_side == Side::left) {
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_construct_left(std::move(
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rhs._left)); // NOLINT(cppcoreguidelines-pro-type-union-access)
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} else {
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_construct_right(std::move(
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rhs._right)); // NOLINT(cppcoreguidelines-pro-type-union-access)
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}
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return *this;
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}
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bool is_left() const noexcept {
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return _side == Side::left;
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}
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bool is_right() const noexcept {
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return _side == Side::right;
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}
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const Left& left() const& {
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if (C10_UNLIKELY(!is_left())) {
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throw std::logic_error(
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"Tried to get left side of an either which is right.");
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}
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return _left; // NOLINT(cppcoreguidelines-pro-type-union-access)
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}
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Left& left() & {
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return const_cast<Left&>(
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const_cast<const either<Left, Right>*>(this)->left());
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}
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Left&& left() && {
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return std::move(left());
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}
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const Right& right() const& {
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if (C10_UNLIKELY(!is_right())) {
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throw std::logic_error(
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"Tried to get right side of an either which is left.");
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}
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return _right; // NOLINT(cppcoreguidelines-pro-type-union-access)
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}
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Right& right() & {
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return const_cast<Right&>(
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const_cast<const either<Left, Right>*>(this)->right());
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}
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Right&& right() && {
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return std::move(right());
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}
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template<class Result, class LeftMapFunc, class RightMapFunc>
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Result map(LeftMapFunc&& leftMapFunc, RightMapFunc&& rightMapFunc) const {
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if (Side::left == _side) {
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return std::forward<LeftMapFunc>(leftMapFunc)(_left);
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} else {
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return std::forward<RightMapFunc>(rightMapFunc)(_right);
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}
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}
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private:
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union {
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Left _left;
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Right _right;
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};
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enum class Side : uint8_t { left, right } _side;
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explicit either(Side side) noexcept : _side(side) {}
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template <typename... Args>
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void _construct_left(Args&&... args) {
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new (&_left) Left(std::forward<Args>(
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args)...); // NOLINT(cppcoreguidelines-pro-type-union-access)
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}
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template <typename... Args>
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void _construct_right(Args&&... args) {
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new (&_right) Right(std::forward<Args>(
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args)...); // NOLINT(cppcoreguidelines-pro-type-union-access)
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}
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void _destruct() noexcept {
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if (_side == Side::left) {
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_left.~Left(); // NOLINT(cppcoreguidelines-pro-type-union-access)
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} else {
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_right.~Right(); // NOLINT(cppcoreguidelines-pro-type-union-access)
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}
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}
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template <typename Left_, typename Right_, typename... Args>
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friend either<Left_, Right_> make_left(Args&&... args);
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template <typename Left_, typename Right_, typename... Args>
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friend either<Left_, Right_> make_right(Args&&... args);
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};
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template <class Left, class Right>
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inline bool operator==(
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const either<Left, Right>& lhs,
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const either<Left, Right>& rhs) {
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if (lhs.is_left() != rhs.is_left()) {
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return false;
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}
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if (lhs.is_left()) {
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return lhs.left() == rhs.left();
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} else {
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return lhs.right() == rhs.right();
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}
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}
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template <class Left, class Right>
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inline bool operator!=(
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const either<Left, Right>& lhs,
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const either<Left, Right>& rhs) {
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return !operator==(lhs, rhs);
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}
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template <class Left, class Right>
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inline std::ostream& operator<<(
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std::ostream& stream,
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const either<Left, Right>& value) {
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if (value.is_left()) {
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stream << "Left(" << value.left() << ")";
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} else {
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stream << "Right(" << value.right() << ")";
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}
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return stream;
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}
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template <typename Left, typename Right, typename... Args>
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inline either<Left, Right> make_left(Args&&... args) {
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either<Left, Right> result(either<Left, Right>::Side::left);
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result._construct_left(std::forward<Args>(args)...);
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return result;
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}
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template <typename Left, typename Right, typename... Args>
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inline either<Left, Right> make_right(Args&&... args) {
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either<Left, Right> result(either<Left, Right>::Side::right);
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result._construct_right(std::forward<Args>(args)...);
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return result;
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}
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} // namespace c10
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