libcryfs/either.h

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#pragma once
#ifndef MESSMER_CPP_UTILS_EITHER_H
#define MESSMER_CPP_UTILS_EITHER_H
#include <boost/optional.hpp>
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namespace cpputils {
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): _side(Side::left) {
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_construct_left(left);
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}
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either(Left &&left): _side(Side::left) {
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_construct_left(std::move(left));
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}
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either(const Right &right): _side(Side::right) {
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_construct_right(right);
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}
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either(Right &&right): _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): _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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either(either<Left, Right> &&rhs): _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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~either() {
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_destruct();
}
//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) {
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_destruct();
_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) {
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_destruct();
_side = rhs._side;
if (_side == Side::left) {
_construct_left(std::move(rhs._left));
} else {
_construct_right(std::move(rhs._right));
}
return *this;
}
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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 {
return _side == Side::left;
}
bool is_right() const {
return _side == Side::right;
}
const Left &left() const& {
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return _left;
}
Left &left() & {
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return const_cast<Left&>(const_cast<const either<Left, Right>*>(this)->left());
}
Left &&left() && {
return std::move(left());
}
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const Right &right() const& {
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return _right;
}
Right &right() & {
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return const_cast<Right&>(const_cast<const either<Left, Right>*>(this)->right());
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}
Right &&right() && {
return std::move(right());
}
boost::optional<const Left&> left_opt() const& {
if (_side == Side::left) {
return _left;
} else {
return boost::none;
}
}
boost::optional<Left&> left_opt() & {
if (_side == Side::left) {
return _left;
} else {
return boost::none;
}
}
boost::optional<Left> left_opt() && {
if (_side == Side::left) {
return std::move(_left);
} else {
return boost::none;
}
}
boost::optional<const Right&> right_opt() const& {
if (_side == Side::right) {
return _right;
} else {
return boost::none;
}
}
boost::optional<Right&> right_opt() & {
if (_side == Side::right) {
return _right;
} else {
return boost::none;
}
}
boost::optional<Right> right_opt() && {
if (_side == Side::right) {
return std::move(_right);
} else {
return boost::none;
}
}
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private:
union {
Left _left;
Right _right;
};
enum class Side : unsigned char {left, right} _side;
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either(Side side): _side(side) {}
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template<typename... Args>
void _construct_left(Args&&... args) {
new(&_left)Left(std::forward<Args>(args)...);
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}
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template<typename... Args>
void _construct_right(Args&&... args) {
new(&_right)Right(std::forward<Args>(args)...);
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}
void _destruct() {
if (_side == Side::left) {
_left.~Left();
} else {
_right.~Right();
}
}
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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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bool operator==(const either<Left, Right> &lhs, const either<Left, Right> &rhs) {
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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>
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bool operator!=(const either<Left, Right> &lhs, const either<Left, Right> &rhs) {
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return !operator==(lhs, rhs);
}
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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()) {
stream << "Left(" << value.left() << ")";
} else {
stream << "Right(" << value.right() << ")";
}
return stream;
}
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template<typename Left, typename Right, typename... Args>
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either<Left, Right> make_left(Args&&... args) {
either<Left, Right> result(either<Left, Right>::Side::left);
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result._construct_left(std::forward<Args>(args)...);
return result;
}
template<typename Left, typename Right, typename... Args>
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either<Left, Right> make_right(Args&&... args) {
either<Left, Right> result(either<Left, Right>::Side::right);
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result._construct_right(std::forward<Args>(args)...);
return result;
}
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}
#endif