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