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+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef PDFIUM_THIRD_PARTY_BASE_OPTIONAL_H_
+#define PDFIUM_THIRD_PARTY_BASE_OPTIONAL_H_
+
+#include <type_traits>
+
+#include "third_party/base/logging.h"
+
+namespace pdfium {
+
+// Specification:
+// http://en.cppreference.com/w/cpp/utility/optional/in_place_t
+struct in_place_t {};
+
+// Specification:
+// http://en.cppreference.com/w/cpp/utility/optional/nullopt_t
+struct nullopt_t {
+ constexpr explicit nullopt_t(int) {}
+};
+
+// Specification:
+// http://en.cppreference.com/w/cpp/utility/optional/in_place
+constexpr in_place_t in_place = {};
+
+// Specification:
+// http://en.cppreference.com/w/cpp/utility/optional/nullopt
+constexpr nullopt_t nullopt(0);
+
+namespace internal {
+
+template <typename T, bool = std::is_trivially_destructible<T>::value>
+struct OptionalStorage {
+ // Initializing |empty_| here instead of using default member initializing
+ // to avoid errors in g++ 4.8.
+ constexpr OptionalStorage() : empty_('\0') {}
+
+ constexpr explicit OptionalStorage(const T& value)
+ : is_null_(false), value_(value) {}
+
+ // TODO(alshabalin): Can't use 'constexpr' with std::move until C++14.
+ explicit OptionalStorage(T&& value)
+ : is_null_(false), value_(std::move(value)) {}
+
+ // TODO(alshabalin): Can't use 'constexpr' with std::forward until C++14.
+ template <class... Args>
+ explicit OptionalStorage(in_place_t, Args&&... args)
+ : is_null_(false), value_(std::forward<Args>(args)...) {}
+
+ // When T is not trivially destructible we must call its
+ // destructor before deallocating its memory.
+ ~OptionalStorage() {
+ if (!is_null_)
+ value_.~T();
+ }
+
+ bool is_null_ = true;
+ union {
+ // |empty_| exists so that the union will always be initialized, even when
+ // it doesn't contain a value. Union members must be initialized for the
+ // constructor to be 'constexpr'.
+ char empty_;
+ T value_;
+ };
+};
+
+template <typename T>
+struct OptionalStorage<T, true> {
+ // Initializing |empty_| here instead of using default member initializing
+ // to avoid errors in g++ 4.8.
+ constexpr OptionalStorage() : empty_('\0') {}
+
+ constexpr explicit OptionalStorage(const T& value)
+ : is_null_(false), value_(value) {}
+
+ // TODO(alshabalin): Can't use 'constexpr' with std::move until C++14.
+ explicit OptionalStorage(T&& value)
+ : is_null_(false), value_(std::move(value)) {}
+
+ // TODO(alshabalin): Can't use 'constexpr' with std::forward until C++14.
+ template <class... Args>
+ explicit OptionalStorage(in_place_t, Args&&... args)
+ : is_null_(false), value_(std::forward<Args>(args)...) {}
+
+ // When T is trivially destructible (i.e. its destructor does nothing) there
+ // is no need to call it. Explicitly defaulting the destructor means it's not
+ // user-provided. Those two together make this destructor trivial.
+ ~OptionalStorage() = default;
+
+ bool is_null_ = true;
+ union {
+ // |empty_| exists so that the union will always be initialized, even when
+ // it doesn't contain a value. Union members must be initialized for the
+ // constructor to be 'constexpr'.
+ char empty_;
+ T value_;
+ };
+};
+
+} // namespace internal
+
+// pdfium::Optional is a PDFium version of the C++17 optional class,
+// based on the Chromium version:
+// std::optional documentation:
+// http://en.cppreference.com/w/cpp/utility/optional
+// Chromium documentation:
+// https://chromium.googlesource.com/chromium/src/+/master/docs/optional.md
+//
+// These are the differences between the specification and the implementation:
+// - The constructor and emplace method using initializer_list are not
+// implemented because 'initializer_list' is banned from Chromium.
+// - Constructors do not use 'constexpr' as it is a C++14 extension.
+// - 'constexpr' might be missing in some places for reasons specified locally.
+// - No exceptions are thrown, because they are banned from Chromium.
+// - All the non-members are in the 'pdifum' namespace instead of 'std'.
+template <typename T>
+class Optional {
+ public:
+ using value_type = T;
+
+ constexpr Optional() {}
+
+ constexpr Optional(nullopt_t) {}
+
+ Optional(const Optional& other) {
+ if (!other.storage_.is_null_)
+ Init(other.value());
+ }
+
+ Optional(Optional&& other) {
+ if (!other.storage_.is_null_)
+ Init(std::move(other.value()));
+ }
+
+ constexpr Optional(const T& value) : storage_(value) {}
+
+ // TODO(alshabalin): Can't use 'constexpr' with std::move until C++14.
+ Optional(T&& value) : storage_(std::move(value)) {}
+
+ // TODO(alshabalin): Can't use 'constexpr' with std::forward until C++14.
+ template <class... Args>
+ explicit Optional(in_place_t, Args&&... args)
+ : storage_(in_place, std::forward<Args>(args)...) {}
+
+ ~Optional() = default;
+
+ Optional& operator=(nullopt_t) {
+ FreeIfNeeded();
+ return *this;
+ }
+
+ Optional& operator=(const Optional& other) {
+ if (other.storage_.is_null_) {
+ FreeIfNeeded();
+ return *this;
+ }
+
+ InitOrAssign(other.value());
+ return *this;
+ }
+
+ Optional& operator=(Optional&& other) {
+ if (other.storage_.is_null_) {
+ FreeIfNeeded();
+ return *this;
+ }
+
+ InitOrAssign(std::move(other.value()));
+ return *this;
+ }
+
+ template <class U>
+ typename std::enable_if<std::is_same<std::decay<U>, T>::value,
+ Optional&>::type
+ operator=(U&& value) {
+ InitOrAssign(std::forward<U>(value));
+ return *this;
+ }
+
+ // TODO(mlamouri): can't use 'constexpr' with DCHECK.
+ const T* operator->() const {
+ DCHECK(!storage_.is_null_);
+ return &value();
+ }
+
+ // TODO(mlamouri): using 'constexpr' here breaks compiler that assume it was
+ // meant to be 'constexpr const'.
+ T* operator->() {
+ DCHECK(!storage_.is_null_);
+ return &value();
+ }
+
+ constexpr const T& operator*() const& { return value(); }
+
+ // TODO(mlamouri): using 'constexpr' here breaks compiler that assume it was
+ // meant to be 'constexpr const'.
+ T& operator*() & { return value(); }
+
+ constexpr const T&& operator*() const&& { return std::move(value()); }
+
+ // TODO(mlamouri): using 'constexpr' here breaks compiler that assume it was
+ // meant to be 'constexpr const'.
+ T&& operator*() && { return std::move(value()); }
+
+ constexpr explicit operator bool() const { return !storage_.is_null_; }
+
+ constexpr bool has_value() const { return !storage_.is_null_; }
+
+ // TODO(mlamouri): using 'constexpr' here breaks compiler that assume it was
+ // meant to be 'constexpr const'.
+ T& value() & {
+ DCHECK(!storage_.is_null_);
+ return storage_.value_;
+ }
+
+ // TODO(mlamouri): can't use 'constexpr' with DCHECK.
+ const T& value() const& {
+ DCHECK(!storage_.is_null_);
+ return storage_.value_;
+ }
+
+ // TODO(mlamouri): using 'constexpr' here breaks compiler that assume it was
+ // meant to be 'constexpr const'.
+ T&& value() && {
+ DCHECK(!storage_.is_null_);
+ return std::move(storage_.value_);
+ }
+
+ // TODO(mlamouri): can't use 'constexpr' with DCHECK.
+ const T&& value() const&& {
+ DCHECK(!storage_.is_null_);
+ return std::move(storage_.value_);
+ }
+
+ template <class U>
+ constexpr T value_or(U&& default_value) const& {
+ // TODO(mlamouri): add the following assert when possible:
+ // static_assert(std::is_copy_constructible<T>::value,
+ // "T must be copy constructible");
+ static_assert(std::is_convertible<U, T>::value,
+ "U must be convertible to T");
+ return storage_.is_null_ ? static_cast<T>(std::forward<U>(default_value))
+ : value();
+ }
+
+ template <class U>
+ T value_or(U&& default_value) && {
+ // TODO(mlamouri): add the following assert when possible:
+ // static_assert(std::is_move_constructible<T>::value,
+ // "T must be move constructible");
+ static_assert(std::is_convertible<U, T>::value,
+ "U must be convertible to T");
+ return storage_.is_null_ ? static_cast<T>(std::forward<U>(default_value))
+ : std::move(value());
+ }
+
+ void swap(Optional& other) {
+ if (storage_.is_null_ && other.storage_.is_null_)
+ return;
+
+ if (storage_.is_null_ != other.storage_.is_null_) {
+ if (storage_.is_null_) {
+ Init(std::move(other.storage_.value_));
+ other.FreeIfNeeded();
+ } else {
+ other.Init(std::move(storage_.value_));
+ FreeIfNeeded();
+ }
+ return;
+ }
+
+ DCHECK(!storage_.is_null_ && !other.storage_.is_null_);
+ using std::swap;
+ swap(**this, *other);
+ }
+
+ void reset() {
+ FreeIfNeeded();
+ }
+
+ template <class... Args>
+ void emplace(Args&&... args) {
+ FreeIfNeeded();
+ Init(std::forward<Args>(args)...);
+ }
+
+ private:
+ void Init(const T& value) {
+ DCHECK(storage_.is_null_);
+ new (&storage_.value_) T(value);
+ storage_.is_null_ = false;
+ }
+
+ void Init(T&& value) {
+ DCHECK(storage_.is_null_);
+ new (&storage_.value_) T(std::move(value));
+ storage_.is_null_ = false;
+ }
+
+ template <class... Args>
+ void Init(Args&&... args) {
+ DCHECK(storage_.is_null_);
+ new (&storage_.value_) T(std::forward<Args>(args)...);
+ storage_.is_null_ = false;
+ }
+
+ void InitOrAssign(const T& value) {
+ if (storage_.is_null_)
+ Init(value);
+ else
+ storage_.value_ = value;
+ }
+
+ void InitOrAssign(T&& value) {
+ if (storage_.is_null_)
+ Init(std::move(value));
+ else
+ storage_.value_ = std::move(value);
+ }
+
+ void FreeIfNeeded() {
+ if (storage_.is_null_)
+ return;
+ storage_.value_.~T();
+ storage_.is_null_ = true;
+ }
+
+ internal::OptionalStorage<T> storage_;
+};
+
+template <class T>
+constexpr bool operator==(const Optional<T>& lhs, const Optional<T>& rhs) {
+ return !!lhs != !!rhs ? false : lhs == nullopt || (*lhs == *rhs);
+}
+
+template <class T>
+constexpr bool operator!=(const Optional<T>& lhs, const Optional<T>& rhs) {
+ return !(lhs == rhs);
+}
+
+template <class T>
+constexpr bool operator<(const Optional<T>& lhs, const Optional<T>& rhs) {
+ return rhs == nullopt ? false : (lhs == nullopt ? true : *lhs < *rhs);
+}
+
+template <class T>
+constexpr bool operator<=(const Optional<T>& lhs, const Optional<T>& rhs) {
+ return !(rhs < lhs);
+}
+
+template <class T>
+constexpr bool operator>(const Optional<T>& lhs, const Optional<T>& rhs) {
+ return rhs < lhs;
+}
+
+template <class T>
+constexpr bool operator>=(const Optional<T>& lhs, const Optional<T>& rhs) {
+ return !(lhs < rhs);
+}
+
+template <class T>
+constexpr bool operator==(const Optional<T>& opt, nullopt_t) {
+ return !opt;
+}
+
+template <class T>
+constexpr bool operator==(nullopt_t, const Optional<T>& opt) {
+ return !opt;
+}
+
+template <class T>
+constexpr bool operator!=(const Optional<T>& opt, nullopt_t) {
+ return !!opt;
+}
+
+template <class T>
+constexpr bool operator!=(nullopt_t, const Optional<T>& opt) {
+ return !!opt;
+}
+
+template <class T>
+constexpr bool operator<(const Optional<T>& opt, nullopt_t) {
+ return false;
+}
+
+template <class T>
+constexpr bool operator<(nullopt_t, const Optional<T>& opt) {
+ return !!opt;
+}
+
+template <class T>
+constexpr bool operator<=(const Optional<T>& opt, nullopt_t) {
+ return !opt;
+}
+
+template <class T>
+constexpr bool operator<=(nullopt_t, const Optional<T>& opt) {
+ return true;
+}
+
+template <class T>
+constexpr bool operator>(const Optional<T>& opt, nullopt_t) {
+ return !!opt;
+}
+
+template <class T>
+constexpr bool operator>(nullopt_t, const Optional<T>& opt) {
+ return false;
+}
+
+template <class T>
+constexpr bool operator>=(const Optional<T>& opt, nullopt_t) {
+ return true;
+}
+
+template <class T>
+constexpr bool operator>=(nullopt_t, const Optional<T>& opt) {
+ return !opt;
+}
+
+template <class T>
+constexpr bool operator==(const Optional<T>& opt, const T& value) {
+ return opt != nullopt ? *opt == value : false;
+}
+
+template <class T>
+constexpr bool operator==(const T& value, const Optional<T>& opt) {
+ return opt == value;
+}
+
+template <class T>
+constexpr bool operator!=(const Optional<T>& opt, const T& value) {
+ return !(opt == value);
+}
+
+template <class T>
+constexpr bool operator!=(const T& value, const Optional<T>& opt) {
+ return !(opt == value);
+}
+
+template <class T>
+constexpr bool operator<(const Optional<T>& opt, const T& value) {
+ return opt != nullopt ? *opt < value : true;
+}
+
+template <class T>
+constexpr bool operator<(const T& value, const Optional<T>& opt) {
+ return opt != nullopt ? value < *opt : false;
+}
+
+template <class T>
+constexpr bool operator<=(const Optional<T>& opt, const T& value) {
+ return !(opt > value);
+}
+
+template <class T>
+constexpr bool operator<=(const T& value, const Optional<T>& opt) {
+ return !(value > opt);
+}
+
+template <class T>
+constexpr bool operator>(const Optional<T>& opt, const T& value) {
+ return value < opt;
+}
+
+template <class T>
+constexpr bool operator>(const T& value, const Optional<T>& opt) {
+ return opt < value;
+}
+
+template <class T>
+constexpr bool operator>=(const Optional<T>& opt, const T& value) {
+ return !(opt < value);
+}
+
+template <class T>
+constexpr bool operator>=(const T& value, const Optional<T>& opt) {
+ return !(value < opt);
+}
+
+template <class T>
+constexpr Optional<typename std::decay<T>::type> make_optional(T&& value) {
+ return Optional<typename std::decay<T>::type>(std::forward<T>(value));
+}
+
+template <class T>
+void swap(Optional<T>& lhs, Optional<T>& rhs) {
+ lhs.swap(rhs);
+}
+
+} // namespace pdfium
+
+namespace std {
+
+template <class T>
+struct hash<pdfium::Optional<T>> {
+ size_t operator()(const pdfium::Optional<T>& opt) const {
+ return opt == pdfium::nullopt ? 0 : std::hash<T>()(*opt);
+ }
+};
+
+} // namespace std
+
+#endif // PDFIUM_THIRD_PARTY_BASE_OPTIONAL_H_
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