[wip] Implement either type
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Sebastian Messmer
parent
e395248f70
commit
187b9ceb53
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#pragma once
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#ifndef MESSMER_CPPUTILS_EITHER_H
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#define MESSMER_CPPUTILS_EITHER_H
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#include <boost/optional.hpp>
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#include <iostream>
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#include "assert/assert.h"
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namespace cpputils {
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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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//TODO Try allowing construction with any type that std::is_convertible to Left or Right.
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either(const Left &left) noexcept(noexcept(std::declval<either<Left, Right>>()._construct_left(left)))
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: _side(Side::left) {
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_construct_left(left);
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}
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either(Left &&left) noexcept(noexcept(std::declval<either<Left, Right>>()._construct_left(std::move(left))))
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: _side(Side::left) {
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_construct_left(std::move(left));
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}
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either(const Right &right) noexcept(noexcept(std::declval<either<Left, Right>>()._construct_right(right)))
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: _side(Side::right) {
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_construct_right(right);
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}
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either(Right &&right) noexcept(noexcept(std::declval<either<Left, Right>>()._construct_right(std::move(right))))
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: _side(Side::right) {
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_construct_right(std::move(right));
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}
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//TODO Try allowing copy-construction when Left/Right types are std::is_convertible
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either(const either<Left, Right> &rhs) noexcept(noexcept(std::declval<either<Left, Right>>()._construct_left(rhs._left)) && noexcept(std::declval<either<Left, Right>>()._construct_right(rhs._right)))
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: _side(rhs._side) {
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if(_side == Side::left) {
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_construct_left(rhs._left);
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} else {
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_construct_right(rhs._right);
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}
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}
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either(either<Left, Right> &&rhs) noexcept(noexcept(_construct_left(std::move(rhs._left))) && noexcept(_construct_right(std::move(rhs._right))))
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: _side(rhs._side) {
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if(_side == Side::left) {
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_construct_left(std::move(rhs._left));
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} else {
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_construct_right(std::move(rhs._right));
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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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//TODO Try allowing copy-assignment when Left/Right types are std::is_convertible
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either<Left, Right> &operator=(const either<Left, Right> &rhs) noexcept(noexcept(_construct_left(rhs._left)) && noexcept(_construct_right(rhs._right))) {
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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(rhs._left);
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} else {
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_construct_right(rhs._right);
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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) noexcept(noexcept(_construct_left(std::move(rhs._left))) && noexcept(_construct_right(std::move(rhs._right)))) {
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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(rhs._left));
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} else {
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_construct_right(std::move(rhs._right));
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}
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return *this;
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}
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//TODO fold, map_left, map_right, left_or_else(val), right_or_else(val), left_or_else(func), right_or_else(func)
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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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ASSERT(is_left(), "Tried to get left side of an either which is right.");
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return _left;
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}
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Left &left() & {
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return const_cast<Left&>(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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ASSERT(is_right(), "Tried to get right side of an either which is left.");
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return _right;
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}
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Right &right() & {
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return const_cast<Right&>(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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boost::optional<const Left&> left_opt() const& noexcept {
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if (_side == Side::left) {
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return _left;
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} else {
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return boost::none;
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}
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}
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boost::optional<Left&> left_opt() & noexcept {
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if (_side == Side::left) {
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return _left;
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} else {
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return boost::none;
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}
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}
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boost::optional<Left> left_opt() && noexcept {
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if (_side == Side::left) {
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return std::move(_left);
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} else {
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return boost::none;
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}
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}
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boost::optional<const Right&> right_opt() const& noexcept {
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if (_side == Side::right) {
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return _right;
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} else {
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return boost::none;
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}
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}
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boost::optional<Right&> right_opt() & noexcept {
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if (_side == Side::right) {
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return _right;
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} else {
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return boost::none;
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}
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}
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boost::optional<Right> right_opt() && noexcept {
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if (_side == Side::right) {
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return std::move(_right);
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} else {
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return boost::none;
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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) noexcept(noexcept(new Left(std::forward<Args>(args)...))) {
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new(&_left)Left(std::forward<Args>(args)...);
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}
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template<typename... Args>
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void _construct_right(Args&&... args) noexcept(noexcept(new Right(std::forward<Args>(args)...))) {
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new(&_right)Right(std::forward<Args>(args)...);
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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();
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} else {
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_right.~Right();
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}
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}
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template<class... Args> static constexpr bool left_noexcept_constructible(Args&&... args) {
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return noexcept(_construct_left(std::forward<Args>(args)...));
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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) noexcept(noexcept(std::declval<either<Left, Right>>()._construct_left(std::forward<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) noexcept(noexcept(std::declval<either<Left, Right>>()._construct_right(std::forward<Args>(args)...)));
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};
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template<class Left, class Right>
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bool operator==(const either<Left, Right> &lhs, const either<Left, Right> &rhs) noexcept(noexcept(std::declval<Left>() == std::declval<Left>()) && noexcept(std::declval<Right>() == std::declval<Right>())) {
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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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bool operator!=(const either<Left, Right> &lhs, const either<Left, Right> &rhs) noexcept(noexcept(operator==(lhs, 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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std::ostream &operator<<(std::ostream &stream, 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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either<Left, Right> make_left(Args&&... args) noexcept(noexcept(std::declval<either<Left, Right>>()._construct_left(std::forward<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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either<Left, Right> make_right(Args&&... args) noexcept(noexcept(std::declval<either<Left, Right>>()._construct_right(std::forward<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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}
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#endif
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@ -54,6 +54,7 @@ set(SOURCES
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system/HomedirTest.cpp
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system/EnvTest.cpp
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value_type/ValueTypeTest.cpp
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either_test.cpp
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)
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add_executable(${PROJECT_NAME}_exit_status process/exit_status.cpp)
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@ -0,0 +1,128 @@
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#include <cpp-utils/either.h>
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#include <gtest/gtest.h>
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using std::string;
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using cpputils::either;
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using cpputils::make_left;
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using cpputils::make_right;
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namespace {
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class MovableOnly final {
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public:
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explicit MovableOnly(int value): _value(value) {}
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MovableOnly(const MovableOnly&) = delete;
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MovableOnly(MovableOnly&&) = default;
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MovableOnly& operator=(const MovableOnly&) = delete;
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MovableOnly& operator=(MovableOnly&&) = default;
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int value() {
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return _value;
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}
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private:
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int _value;
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};
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}
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TEST(EitherTest, givenLeft_thenIsLeft) {
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either<int, string> a(4);
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EXPECT_TRUE(a.is_left());
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}
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TEST(EitherTest, givenLeft_thenIsNotRight) {
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either<int, string> a(4);
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EXPECT_FALSE(a.is_right());
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}
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TEST(EitherTest, givenLeft_whenQueryingLeft_thenValueIsCorrect) {
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either<int, string> a(4);
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EXPECT_EQ(4, a.left());
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}
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TEST(EitherTest, givenLeft_whenQueryingRight_thenThrows) {
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either<int, string> a(4);
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EXPECT_ANY_THROW(a.right());
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}
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TEST(EitherTest, givenLeft_whenQueryingOptLeft_thenValueIsCorrect) {
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either<int, string> a(4);
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EXPECT_EQ(4, a.left_opt().value());
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}
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TEST(EitherTest, givenLeft_whenQueryingOptRight_thenIsNone) {
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either<int, string> a(4);
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EXPECT_EQ(boost::none, a.right_opt());
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}
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TEST(EitherTest, givenRight_thenIsRight) {
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either<int, string> a("4");
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EXPECT_TRUE(a.is_right());
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}
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TEST(EitherTest, givenRight_thenIsNotLeft) {
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either<int, string> a("4");
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EXPECT_FALSE(a.is_left());
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}
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TEST(EitherTest, givenRight_whenQueryingRight_thenValueIsCorrect) {
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either<int, string> a("4");
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EXPECT_EQ("4", a.right());
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}
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TEST(EitherTest, givenRight_whenQueryingLeft_thenThrows) {
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either<int, string> a("4");
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EXPECT_ANY_THROW(a.left());
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}
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TEST(EitherTest, givenRight_whenQueryingRightOpt_thenValueIsCorrect) {
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either<int, string> a("4");
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EXPECT_EQ("4", a.right_opt().value());
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}
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TEST(EitherTest, givenRight_whenQueryingLeftOpt_thenThrows) {
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either<int, string> a("4");
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EXPECT_EQ(boost::none, a.left_opt());
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}
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TEST(EitherTest, whenCopyConstructingLeft_thenValueIsCorrect) {
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string a = "4";
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either<string, int> b(a);
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EXPECT_EQ(a, b.left());
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}
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TEST(EitherTest, whenMoveConstructingLeft_thenValueIsCorrect) {
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string a = "4";
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either<string, int> b(std::move(a));
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EXPECT_EQ("4", b.left());
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}
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TEST(EitherTest, whenCopyConstructingRight_thenValueIsCorrect) {
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string a = "4";
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either<int, string> b(a);
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EXPECT_EQ(a, b.right());
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}
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TEST(EitherTest, whenMoveConstructingRight_thenValueIsCorrect) {
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string a = "4";
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either<int, string> b(std::move(a));
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EXPECT_EQ("4", b.right());
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}
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//TEST(EitherTest, whenMakingLeft_thenIsLeft) {
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// auto a = make_left<int, string>(4);
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// EXPECT_TRUE(a.is_left());
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//}
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//
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//TEST(EitherTest, whenMakingRight_thenIsRight) {
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// auto a = make_right<int, string>("4");
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// EXPECT_TRUE(a.is_right());
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//}
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// TODO Test MovableOnly content type
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// TODO Test Left == Right (Same type)
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// TODO Test operator== and !=
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// TODO Test copy/move constructor
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// TODO Test destruction
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// TODO Test make_left / make_right
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// TODO Test noexcept tags are correct
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@ -9,6 +9,8 @@ using cpputils::value_type::OrderedIdValueType;
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using cpputils::value_type::QuantityValueType;
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using cpputils::value_type::FlagsValueType;
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// TODO Test that noexcept flags are set correctly
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namespace {
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struct MyIdValueType : IdValueType<MyIdValueType, int64_t> {
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