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Initial implementation of error_or

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3  NOTICE
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+error_or
+ Copyright 2012 Andrew C. Morrow
+
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278 error_or.hpp
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+// Copyright 2012 Andrew C. Morrow
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef included_108FBB04_F426_414D_9EDD_B4D2AF941E96
+#define included_108FBB04_F426_414D_9EDD_B4D2AF941E96
+
+#include <cassert>
+#include <initializer_list>
+#include <memory>
+#include <system_error>
+#include <type_traits>
+
+namespace acm {
+
+ namespace detail {
+
+ namespace adl_swap_ns {
+ using std::swap;
+
+ template <class T>
+ struct is_nothrow_swappable_test {
+ static bool constexpr value = noexcept(swap(std::declval<T&>(), std::declval<T&>()));
+ };
+ } // namespace adl_swap_ns
+
+ // This really should be part of C++
+ template <class T>
+ struct is_nothrow_swappable
+ : std::integral_constant<bool, adl_swap_ns::is_nothrow_swappable_test<T>::value>
+ {};
+
+ } // namespace detail
+
+ template<typename E, typename T>
+ class error_or {
+
+ public:
+ using error_type = E;
+ using value_type = T;
+
+ inline error_or() noexcept(std::is_nothrow_default_constructible<value_type>::value) {
+ new(&val_.value) value_type;
+ }
+
+ inline error_or(error_type error) noexcept(std::is_nothrow_move_constructible<error_type>::value)
+ : ok_(false) {
+ assert(error);
+ new(&val_.error) error_type(std::move(error));
+ }
+
+ inline error_or(value_type value) noexcept(std::is_nothrow_move_constructible<value_type>::value) {
+ new(&val_.value) value_type(std::move(value));
+ }
+
+ template<typename U = value_type>
+ inline error_or(std::initializer_list<typename U::value_type> values) noexcept(std::is_nothrow_constructible<U, std::initializer_list<typename U::value_type>>::value) {
+ new(&val_.value) value_type(values);
+ }
+
+ // template<typename... Args>
+ // inline error_or(Args&&... args) noexcept(std::is_nothrow_constructible<value_type, Args...>::value)
+ // {
+ // new(&val_.value) value_type(std::forward<Args>(args)...);
+ // }
+
+ inline error_or(const error_or& other) noexcept(std::is_nothrow_copy_constructible<error_type>::value and
+ std::is_nothrow_copy_constructible<value_type>::value) {
+ if (other.ok_)
+ new(&val_.value) value_type(other.val_.value);
+ else
+ new(&val_.error) error_type(other.val_.error);
+ ok_ = other.ok_;
+ }
+
+ inline error_or(error_or&& other) noexcept((std::is_nothrow_move_constructible<error_type>::value or
+ std::is_nothrow_copy_constructible<error_type>::value) and
+ (std::is_nothrow_copy_constructible<value_type>::value or
+ std::is_nothrow_copy_constructible<value_type>::value)) {
+ if (other.ok_)
+ new(&val_.value) value_type(std::move_if_noexcept(other.val_.value));
+ else
+ new(&val_.error) error_type(std::move_if_noexcept(other.val_.error));
+ ok_ = other.ok_;
+ }
+
+ template<typename U>
+ inline error_or(const error_or<error_type, U>& other) noexcept(std::is_nothrow_copy_constructible<error_type>::value and
+ std::is_nothrow_copy_constructible<value_type>::value) {
+ if (other.ok_)
+ new(&val_.value) value_type(other.val_.value);
+ else
+ new(&val_.error) error_type(other.val_.error);
+ ok_ = other.ok_;
+ }
+
+ template<typename U>
+ inline error_or(error_or<error_type, U>&& other) noexcept((std::is_nothrow_move_constructible<error_type>::value or
+ std::is_nothrow_copy_constructible<error_type>::value) and
+ (std::is_nothrow_constructible<value_type, typename std::add_rvalue_reference<U>::type>::value or
+ std::is_nothrow_constructible<value_type, typename std::add_lvalue_reference<U>::type>::value)) {
+ if (other.ok_)
+ new(&val_.value) value_type(move_if_noexcept_from(other.val_.value));
+ else
+ new(&val_.error) error_type(std::move_if_noexcept(other.val_.error));
+ ok_ = other.ok_;
+ }
+
+ void swap(error_or& other) noexcept {
+ other.sfinae_swap(*this);
+ }
+
+ friend inline void swap(error_or& a, error_or& b) noexcept {
+ a.swap(b);
+ }
+
+ inline error_or& operator=(error_type error) noexcept(std::is_nothrow_constructible<error_or, typename std::add_rvalue_reference<error_type>::type>::value) {
+ error_or(std::move(error)).swap(*this);
+ return *this;
+ }
+
+ inline error_or& operator=(value_type value) noexcept(std::is_nothrow_constructible<error_or, typename std::add_rvalue_reference<value_type>::type>::value) {
+ error_or(std::move(value)).swap(*this);
+ return *this;
+ }
+
+ inline error_or& operator=(error_or other) noexcept(std::is_nothrow_move_constructible<error_or>::value) {
+ error_or(std::move(other)).swap(*this);
+ return *this;
+ }
+
+ template<typename U>
+ inline error_or& operator=(error_or<error_type, U> other) noexcept(std::is_nothrow_constructible<error_or, error_or<E, U>&&>::value) {
+ error_or(std::move(other)).swap(*this);
+ return *this;
+ }
+
+ inline ~error_or() noexcept(std::is_nothrow_destructible<error_type>::value and
+ std::is_nothrow_destructible<value_type>::value) {
+ if (ok_)
+ val_.value.~value_type();
+ else
+ val_.error.~error_type();
+ }
+
+ inline bool ok() const noexcept {
+ return ok_;
+ }
+
+ inline explicit operator bool() const noexcept {
+ return ok_;
+ }
+
+ inline const error_type& error() const noexcept {
+ assert(!ok_);
+ return val_.error;
+ }
+
+ inline value_type& value() noexcept {
+ assert(ok_);
+ return val_.value;
+ }
+
+ inline const value_type& value() const noexcept {
+ assert(ok_);
+ return val_.value;
+ }
+
+ inline error_type&& release_error() noexcept {
+ assert(!ok_);
+ return std::move(val_.error);
+ }
+
+ inline value_type&& release_value() noexcept {
+ assert(ok_);
+ return std::move(val_.value);
+ }
+
+ private:
+ union val {
+ // The lifecycle of members is handled by the enclosing class.
+ inline val() noexcept {}
+ inline ~val() noexcept {}
+ value_type value;
+ error_type error;
+ } val_;
+
+ bool ok_ = true;
+
+ static constexpr bool is_nothrow_swappable =
+ detail::is_nothrow_swappable<error_type>::value and
+ detail::is_nothrow_swappable<value_type>::value and
+ std::is_nothrow_move_constructible<error_type>::value and
+ std::is_nothrow_move_constructible<value_type>::value and
+ std::is_nothrow_destructible<error_type>::value and
+ std::is_nothrow_destructible<value_type>::value;
+
+ template<typename U = value_type>
+ typename std::enable_if<error_or<error_type, U>::is_nothrow_swappable>::type sfinae_swap(error_or& other) noexcept {
+ using std::swap;
+
+ if (ok_ == other.ok_) {
+ if (ok_)
+ swap(val_.value, other.val_.value);
+ else
+ swap(val_.error, other.val_.error);
+ } else {
+ if (ok_) {
+ new(&val_.error) error_type(std::move(other.val_.error));
+ new(&other.val_.value) T(std::move(val_.value));
+ val_.value.~T();
+ other.val_.error.~error_type();
+ } else {
+ new(&other.val_.error) error_type(std::move(val_.error));
+ new(&val_.value) T(std::move(other.val_.value));
+ other.val_.value.~T();
+ val_.error.~error_type();
+ }
+ swap(ok_, other.ok_);
+ }
+ }
+
+ template<typename U>
+ typename std::conditional
+ <
+ !std::is_nothrow_constructible<T, typename std::add_rvalue_reference<U>::type>::value and std::is_constructible<U, typename std::add_lvalue_reference<U>::type>::value,
+ const T&,
+ T&&
+ >::type
+ move_if_noexcept_from(U& u) {
+ return std::move(u);
+ }
+
+ };
+
+ template<typename E1, typename T1, typename E2, typename T2>
+ bool operator==(const error_or<E1, T1>& lhs, const error_or<E2, T2>& rhs) noexcept(noexcept(lhs.value() == rhs.value()) and
+ noexcept(lhs.error() == rhs.error())) {
+ if (lhs.ok() == rhs.ok()) {
+ if (lhs.ok()) {
+ return lhs.value() == rhs.value();
+ } else {
+ return lhs.error() == rhs.error();
+ }
+ }
+ return false;
+ }
+
+ template<typename E1, typename T1, typename E2, typename T2>
+ bool operator!=(const error_or<E1, T1>& lhs, const error_or<E2, T2>& rhs) noexcept(noexcept(lhs == rhs)) {
+ return not lhs == rhs;
+ }
+
+ template<typename T>
+ using error_code_or = error_or<std::error_code, T>;
+
+ template<typename T>
+ using error_condition_or = error_or<std::error_condition, T>;
+
+ template<typename T>
+ using error_code_or_unique = error_code_or<std::unique_ptr<T>>;
+
+ template<typename T>
+ using error_condition_or_unique = error_condition_or<std::unique_ptr<T>>;
+
+} // namespace acm
+
+#endif // included_108FBB04_F426_414D_9EDD_B4D2AF941E96
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