libcryfs/src/cpp-utils/either.h
2020-07-22 10:32:43 -07:00

242 lines
11 KiB
C++

#pragma once
#ifndef MESSMER_CPPUTILS_EITHER_H
#define MESSMER_CPPUTILS_EITHER_H
#include <boost/optional.hpp>
#include <iostream>
#include "assert/assert.h"
namespace cpputils {
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) noexcept(noexcept(std::declval<either<Left, Right>>()._construct_left(std::forward<Head>(construct_left_head_arg), std::forward<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) noexcept(noexcept(std::declval<either<Left, Right>>()._construct_right(std::forward<Head>(construct_right_head_arg), std::forward<Tail>(construct_right_tail_args)...)))
: _side(Side::right) {
_construct_right(std::forward<Head>(construct_right_head_arg), std::forward<Tail>(construct_right_tail_args)...);
}
//TODO Try allowing copy-construction when Left/Right types are std::is_convertible
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)))
: _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(noexcept(std::declval<either<Left, Right>>()._construct_left(std::move(rhs._left))) && noexcept(std::declval<either<Left, Right>>()._construct_right(std::move(rhs._right))))
: _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();
}
//TODO Try allowing copy-assignment when Left/Right types are std::is_convertible
// NOLINTNEXTLINE(cert-oop54-cpp)
either<Left, Right> &operator=(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))) {
if (this == &rhs) {
return *this;
}
_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) noexcept(noexcept(std::declval<either<Left, Right>>()._construct_left(std::move(rhs._left))) && noexcept(std::declval<either<Left, Right>>()._construct_right(std::move(rhs._right)))) {
if (this == &rhs) {
return *this;
}
_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;
}
//TODO fold, map_left, map_right, left_or_else(val), right_or_else(val), left_or_else(func), right_or_else(func)
bool is_left() const noexcept {
return _side == Side::left;
}
bool is_right() const noexcept {
return _side == Side::right;
}
const Left &left() const& {
if (!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 (!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());
}
boost::optional<const Left&> left_opt() const& noexcept {
if (_side == Side::left) {
return _left; // NOLINT(cppcoreguidelines-pro-type-union-access)
} else {
return boost::none;
}
}
boost::optional<Left&> left_opt() & noexcept {
if (_side == Side::left) {
return _left; // NOLINT(cppcoreguidelines-pro-type-union-access)
} else {
return boost::none;
}
}
// warning: opposed to the other left_opt variants, this one already moves the content and returns by value.
boost::optional<Left> left_opt() && noexcept(noexcept(boost::optional<Left>(std::move(std::declval<either<Left, Right>>()._left)))) {
if (_side == Side::left) {
return std::move(_left); // NOLINT(cppcoreguidelines-pro-type-union-access)
} else {
return boost::none;
}
}
boost::optional<const Right&> right_opt() const& noexcept {
if (_side == Side::right) {
return _right; // NOLINT(cppcoreguidelines-pro-type-union-access)
} else {
return boost::none;
}
}
boost::optional<Right&> right_opt() & noexcept {
if (_side == Side::right) {
return _right; // NOLINT(cppcoreguidelines-pro-type-union-access)
} else {
return boost::none;
}
}
// warning: opposed to the other left_opt variants, this one already moves the content and returns by value.
boost::optional<Right> right_opt() && noexcept(noexcept(boost::optional<Right>(std::move(std::declval<either<Left, Right>>()._right)))) {
if (_side == Side::right) {
return std::move(_right); // NOLINT(cppcoreguidelines-pro-type-union-access)
} else {
return boost::none;
}
}
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) noexcept(noexcept(new Left(std::forward<Args>(args)...))) {
new(&_left)Left(std::forward<Args>(args)...); // NOLINT(cppcoreguidelines-pro-type-union-access)
}
template<typename... Args>
void _construct_right(Args&&... args) noexcept(noexcept(new Right(std::forward<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) /* TODO noexcept(noexcept(std::declval<either<Left, Right>>()._construct_left(std::forward<Args>(args)...))) */;
template<typename Left_, typename Right_, typename... Args>
friend either<Left_, Right_> make_right(Args&&... args) /* TODO noexcept(noexcept(std::declval<either<Left, Right>>()._construct_right(std::forward<Args>(args)...))) */;
};
template<class Left, class Right>
inline 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>())) {
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) noexcept(noexcept(operator==(lhs, 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) /* TODO noexcept(noexcept(std::declval<either<Left, Right>>()._construct_left(std::forward<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) /* TODO noexcept(noexcept(std::declval<either<Left, Right>>()._construct_right(std::forward<Args>(args)...))) */ {
either<Left, Right> result(either<Left, Right>::Side::right);
result._construct_right(std::forward<Args>(args)...);
return result;
}
}
#endif