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diff --git a/absl/types/optional.h b/absl/types/optional.h new file mode 100644 index 000000000000..5099d4899d6d --- /dev/null +++ b/absl/types/optional.h @@ -0,0 +1,1092 @@ +// +// Copyright 2017 The Abseil Authors. +// +// 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. +// +// ----------------------------------------------------------------------------- +// optional.h +// ----------------------------------------------------------------------------- +// +// This header file define the `absl::optional` type for holding a value which +// may or may not be present. This type is useful for providing value semantics +// for operations that may either wish to return or hold "something-or-nothing". +// +// Example: +// +// // A common way to signal operation failure is to provide an output +// // parameter and a bool return type: +// bool AcquireResource(const Input&, Resource * out); +// +// // Providing an absl::optional return type provides a cleaner API: +// absl::optional<Resource> AcquireResource(const Input&); +// +// `absl::optional` is a C++11 compatible version of the C++17 `std::optional` +// abstraction and is designed to be a drop-in replacement for code compliant +// with C++17. +#ifndef ABSL_TYPES_OPTIONAL_H_ +#define ABSL_TYPES_OPTIONAL_H_ + +#include "absl/base/config.h" +#include "absl/utility/utility.h" + +#ifdef ABSL_HAVE_STD_OPTIONAL + +#include <optional> + +namespace absl { +using std::bad_optional_access; +using std::optional; +using std::make_optional; +using std::nullopt_t; +using std::nullopt; +} + +#else // ABSL_HAVE_STD_OPTIONAL + +#include <cassert> +#include <functional> +#include <initializer_list> +#include <new> +#include <type_traits> +#include <utility> + +#include "absl/memory/memory.h" +#include "absl/meta/type_traits.h" +#include "absl/types/bad_optional_access.h" + +// ABSL_OPTIONAL_USE_INHERITING_CONSTRUCTORS +// +// Inheriting constructors is supported in GCC 4.8+, Clang 3.3+ and MSVC 2015. +// __cpp_inheriting_constructors is a predefined macro and a recommended way to +// check for this language feature, but GCC doesn't support it until 5.0 and +// Clang doesn't support it until 3.6. +// Also, MSVC 2015 has a bug: it doesn't inherit the constexpr template +// constructor. For example, the following code won't work on MSVC 2015 Update3: +// struct Base { +// int t; +// template <typename T> +// constexpr Base(T t_) : t(t_) {} +// }; +// struct Foo : Base { +// using Base::Base; +// } +// constexpr Foo foo(0); // doesn't work on MSVC 2015 +#if defined(__clang__) +#if __has_feature(cxx_inheriting_constructors) +#define ABSL_OPTIONAL_USE_INHERITING_CONSTRUCTORS 1 +#endif +#elif (defined(__GNUC__) && \ + (__GNUC__ > 4 || __GNUC__ == 4 && __GNUC_MINOR__ >= 8)) || \ + (__cpp_inheriting_constructors >= 200802) || \ + (defined(_MSC_VER) && _MSC_VER >= 1910) +#define ABSL_OPTIONAL_USE_INHERITING_CONSTRUCTORS 1 +#endif + +namespace absl { + +// optional +// +// A value of type `absl::optional<T>` holds either a value of `T` or an +// "empty" value. When it holds a value of `T`, it stores it as a direct +// sub-object, so `sizeof(optional<T>)` is approximately +// `sizeof(T) + sizeof(bool)`. +// +// This implementation is based on the specification in the latest draft of the +// C++17 `std::optional` specification as of May 2017, section 20.6. +// +// Differences between `absl::optional<T>` and `std::optional<T>` include: +// +// * `constexpr` is not used for non-const member functions. +// (dependency on some differences between C++11 and C++14.) +// * `absl::nullopt` and `absl::in_place` are not declared `constexpr`. We +// need the inline variable support in C++17 for external linkage. +// * Throws `absl::bad_optional_access` instead of +// `std::bad_optional_access`. +// * `optional::swap()` and `absl::swap()` relies on +// `std::is_(nothrow_)swappable()`, which has been introduced in C++17. +// As a workaround, we assume `is_swappable()` is always `true` +// and `is_nothrow_swappable()` is the same as `std::is_trivial()`. +// * `make_optional()` cannot be declared `constexpr` due to the absence of +// guaranteed copy elision. +template <typename T> +class optional; + +// nullopt_t +// +// Class type for `absl::nullopt` used to indicate an `absl::optional<T>` type +// that does not contain a value. +struct nullopt_t { + struct init_t {}; + static init_t init; + + // It must not be default-constructible to avoid ambiguity for opt = {}. + // Note the non-const reference, which is to eliminate ambiguity for code + // like: + // + // struct S { int value; }; + // + // void Test() { + // optional<S> opt; + // opt = {{}}; + // } + explicit constexpr nullopt_t(init_t& /*unused*/) {} +}; + +// nullopt +// +// A tag constant of type `absl::nullopt_t` used to indicate an empty +// `absl::optional` in certain functions, such as construction or assignment. +extern const nullopt_t nullopt; + +namespace optional_internal { + +struct empty_struct {}; +// This class stores the data in optional<T>. +// It is specialized based on whether T is trivially destructible. +// This is the specialization for non trivially destructible type. +template <typename T, bool = std::is_trivially_destructible<T>::value> +class optional_data_dtor_base { + struct dummy_type { + static_assert(sizeof(T) % sizeof(empty_struct) == 0, ""); + // Use an array to avoid GCC 6 placement-new warning. + empty_struct data[sizeof(T) / sizeof(empty_struct)]; + }; + + protected: + // Whether there is data or not. + bool engaged_; + // Data storage + union { + dummy_type dummy_; + T data_; + }; + + void destruct() noexcept { + if (engaged_) { + data_.~T(); + engaged_ = false; + } + } + + // dummy_ must be initialized for constexpr constructor. + constexpr optional_data_dtor_base() noexcept : engaged_(false), dummy_{{}} {} + + template <typename... Args> + constexpr explicit optional_data_dtor_base(in_place_t, Args&&... args) + : engaged_(true), data_(absl::forward<Args>(args)...) {} + + ~optional_data_dtor_base() { destruct(); } +}; + +// Specialization for trivially destructible type. +template <typename T> +class optional_data_dtor_base<T, true> { + struct dummy_type { + static_assert(sizeof(T) % sizeof(empty_struct) == 0, ""); + // Use array to avoid GCC 6 placement-new warning. + empty_struct data[sizeof(T) / sizeof(empty_struct)]; + }; + + protected: + // Whether there is data or not. + bool engaged_; + // Data storage + union { + dummy_type dummy_; + T data_; + }; + void destruct() noexcept { engaged_ = false; } + + // dummy_ must be initialized for constexpr constructor. + constexpr optional_data_dtor_base() noexcept : engaged_(false), dummy_{{}} {} + + template <typename... Args> + constexpr explicit optional_data_dtor_base(in_place_t, Args&&... args) + : engaged_(true), data_(absl::forward<Args>(args)...) {} +}; + +template <typename T> +class optional_data_base : public optional_data_dtor_base<T> { + protected: + using base = optional_data_dtor_base<T>; +#if ABSL_OPTIONAL_USE_INHERITING_CONSTRUCTORS + using base::base; +#else + optional_data_base() = default; + + template <typename... Args> + constexpr explicit optional_data_base(in_place_t t, Args&&... args) + : base(t, absl::forward<Args>(args)...) {} +#endif + + template <typename... Args> + void construct(Args&&... args) { + // Use dummy_'s address to work around casting cv-qualified T* to void*. + ::new (static_cast<void*>(&this->dummy_)) T(std::forward<Args>(args)...); + this->engaged_ = true; + } + + template <typename U> + void assign(U&& u) { + if (this->engaged_) { + this->data_ = std::forward<U>(u); + } else { + construct(std::forward<U>(u)); + } + } +}; + +// TODO(b/34201852): Add another base class using +// std::is_trivially_move_constructible trait when available to match +// http://cplusplus.github.io/LWG/lwg-defects.html#2900, for types that +// have trivial move but nontrivial copy. +// Also, we should be checking is_trivially_copyable here, which is not +// supported now, so we use is_trivially_* traits instead. +template <typename T, bool = absl::is_trivially_copy_constructible<T>::value&& + absl::is_trivially_copy_assignable< + typename std::remove_cv<T>::type>::value&& + std::is_trivially_destructible<T>::value> +class optional_data; + +// Trivially copyable types +template <typename T> +class optional_data<T, true> : public optional_data_base<T> { + protected: +#if ABSL_OPTIONAL_USE_INHERITING_CONSTRUCTORS + using optional_data_base<T>::optional_data_base; +#else + optional_data() = default; + + template <typename... Args> + constexpr explicit optional_data(in_place_t t, Args&&... args) + : optional_data_base<T>(t, absl::forward<Args>(args)...) {} +#endif +}; + +template <typename T> +class optional_data<T, false> : public optional_data_base<T> { + protected: +#if ABSL_OPTIONAL_USE_INHERITING_CONSTRUCTORS + using optional_data_base<T>::optional_data_base; +#else + template <typename... Args> + constexpr explicit optional_data(in_place_t t, Args&&... args) + : optional_data_base<T>(t, absl::forward<Args>(args)...) {} +#endif + + optional_data() = default; + + optional_data(const optional_data& rhs) { + if (rhs.engaged_) { + this->construct(rhs.data_); + } + } + + optional_data(optional_data&& rhs) noexcept( + absl::default_allocator_is_nothrow::value || + std::is_nothrow_move_constructible<T>::value) { + if (rhs.engaged_) { + this->construct(std::move(rhs.data_)); + } + } + + optional_data& operator=(const optional_data& rhs) { + if (rhs.engaged_) { + this->assign(rhs.data_); + } else { + this->destruct(); + } + return *this; + } + + optional_data& operator=(optional_data&& rhs) noexcept( + std::is_nothrow_move_assignable<T>::value&& + std::is_nothrow_move_constructible<T>::value) { + if (rhs.engaged_) { + this->assign(std::move(rhs.data_)); + } else { + this->destruct(); + } + return *this; + } +}; + +// Ordered by level of restriction, from low to high. +// Copyable implies movable. +enum class copy_traits { copyable = 0, movable = 1, non_movable = 2 }; + +// Base class for enabling/disabling copy/move constructor. +template <copy_traits> +class optional_ctor_base; + +template <> +class optional_ctor_base<copy_traits::copyable> { + public: + constexpr optional_ctor_base() = default; + optional_ctor_base(const optional_ctor_base&) = default; + optional_ctor_base(optional_ctor_base&&) = default; + optional_ctor_base& operator=(const optional_ctor_base&) = default; + optional_ctor_base& operator=(optional_ctor_base&&) = default; +}; + +template <> +class optional_ctor_base<copy_traits::movable> { + public: + constexpr optional_ctor_base() = default; + optional_ctor_base(const optional_ctor_base&) = delete; + optional_ctor_base(optional_ctor_base&&) = default; + optional_ctor_base& operator=(const optional_ctor_base&) = default; + optional_ctor_base& operator=(optional_ctor_base&&) = default; +}; + +template <> +class optional_ctor_base<copy_traits::non_movable> { + public: + constexpr optional_ctor_base() = default; + optional_ctor_base(const optional_ctor_base&) = delete; + optional_ctor_base(optional_ctor_base&&) = delete; + optional_ctor_base& operator=(const optional_ctor_base&) = default; + optional_ctor_base& operator=(optional_ctor_base&&) = default; +}; + +// Base class for enabling/disabling copy/move assignment. +template <copy_traits> +class optional_assign_base; + +template <> +class optional_assign_base<copy_traits::copyable> { + public: + constexpr optional_assign_base() = default; + optional_assign_base(const optional_assign_base&) = default; + optional_assign_base(optional_assign_base&&) = default; + optional_assign_base& operator=(const optional_assign_base&) = default; + optional_assign_base& operator=(optional_assign_base&&) = default; +}; + +template <> +class optional_assign_base<copy_traits::movable> { + public: + constexpr optional_assign_base() = default; + optional_assign_base(const optional_assign_base&) = default; + optional_assign_base(optional_assign_base&&) = default; + optional_assign_base& operator=(const optional_assign_base&) = delete; + optional_assign_base& operator=(optional_assign_base&&) = default; +}; + +template <> +class optional_assign_base<copy_traits::non_movable> { + public: + constexpr optional_assign_base() = default; + optional_assign_base(const optional_assign_base&) = default; + optional_assign_base(optional_assign_base&&) = default; + optional_assign_base& operator=(const optional_assign_base&) = delete; + optional_assign_base& operator=(optional_assign_base&&) = delete; +}; + +template <typename T> +constexpr copy_traits get_ctor_copy_traits() { + return std::is_copy_constructible<T>::value + ? copy_traits::copyable + : std::is_move_constructible<T>::value ? copy_traits::movable + : copy_traits::non_movable; +} + +template <typename T> +constexpr copy_traits get_assign_copy_traits() { + return std::is_copy_assignable<T>::value && + std::is_copy_constructible<T>::value + ? copy_traits::copyable + : std::is_move_assignable<T>::value && + std::is_move_constructible<T>::value + ? copy_traits::movable + : copy_traits::non_movable; +} + +// Whether T is constructible or convertible from optional<U>. +template <typename T, typename U> +struct is_constructible_convertible_from_optional + : std::integral_constant< + bool, std::is_constructible<T, optional<U>&>::value || + std::is_constructible<T, optional<U>&&>::value || + std::is_constructible<T, const optional<U>&>::value || + std::is_constructible<T, const optional<U>&&>::value || + std::is_convertible<optional<U>&, T>::value || + std::is_convertible<optional<U>&&, T>::value || + std::is_convertible<const optional<U>&, T>::value || + std::is_convertible<const optional<U>&&, T>::value> {}; + +// Whether T is constructible or convertible or assignable from optional<U>. +template <typename T, typename U> +struct is_constructible_convertible_assignable_from_optional + : std::integral_constant< + bool, is_constructible_convertible_from_optional<T, U>::value || + std::is_assignable<T&, optional<U>&>::value || + std::is_assignable<T&, optional<U>&&>::value || + std::is_assignable<T&, const optional<U>&>::value || + std::is_assignable<T&, const optional<U>&&>::value> {}; + +// Helper function used by [optional.relops], [optional.comp_with_t], +// for checking whether an expression is convertible to bool. +bool convertible_to_bool(bool); + +} // namespace optional_internal + +// ----------------------------------------------------------------------------- +// absl::optional class definition +// ----------------------------------------------------------------------------- + +template <typename T> +class optional : private optional_internal::optional_data<T>, + private optional_internal::optional_ctor_base< + optional_internal::get_ctor_copy_traits<T>()>, + private optional_internal::optional_assign_base< + optional_internal::get_assign_copy_traits<T>()> { + using data_base = optional_internal::optional_data<T>; + + public: + typedef T value_type; + + // Constructors + + // Constructs a default-constructed `optional` holding the empty value, NOT a + // default constructed `T`. + constexpr optional() noexcept {} + + // Construct an` optional` initialized with `nullopt` to hold an empty value. + constexpr optional(nullopt_t) noexcept {} // NOLINT(runtime/explicit) + + // Copy constructor, standard semantics + optional(const optional& src) = default; + + // Move constructor, standard semantics + optional(optional&& src) = default; + + // Constructs a non-empty `optional` direct-initialized value of type `T` from + // the arguments `std::forward<Args>(args)...` within the `optional`. + // (The `in_place_t` is a tag used to indicate that the contained object + // should be constructed in-place.) + // TODO(b/34201852): Add std::is_constructible<T, Args&&...> SFINAE. + template <typename... Args> + constexpr explicit optional(in_place_t, Args&&... args) + : data_base(in_place_t(), absl::forward<Args>(args)...) {} + + // Constructs a non-empty `optional' direct-initialized value of type `T` from + // the arguments of an initializer_list and `std::forward<Args>(args)...`. + // (The `in_place_t` is a tag used to indicate that the contained object + // should be constructed in-place.) + template <typename U, typename... Args, + typename = typename std::enable_if<std::is_constructible< + T, std::initializer_list<U>&, Args&&...>::value>::type> + constexpr explicit optional(in_place_t, std::initializer_list<U> il, + Args&&... args) + : data_base(in_place_t(), il, absl::forward<Args>(args)...) { + } + + // Value constructor (implicit) + template < + typename U = T, + typename std::enable_if< + absl::conjunction<absl::negation<std::is_same< + in_place_t, typename std::decay<U>::type> >, + absl::negation<std::is_same< + optional<T>, typename std::decay<U>::type> >, + std::is_convertible<U&&, T>, + std::is_constructible<T, U&&> >::value, + bool>::type = false> + constexpr optional(U&& v) : data_base(in_place_t(), absl::forward<U>(v)) {} + + // Value constructor (explicit) + template < + typename U = T, + typename std::enable_if< + absl::conjunction<absl::negation<std::is_same< + in_place_t, typename std::decay<U>::type>>, + absl::negation<std::is_same< + optional<T>, typename std::decay<U>::type>>, + absl::negation<std::is_convertible<U&&, T>>, + std::is_constructible<T, U&&>>::value, + bool>::type = false> + explicit constexpr optional(U&& v) + : data_base(in_place_t(), absl::forward<U>(v)) {} + + // Converting copy constructor (implicit) + template <typename U, + typename std::enable_if< + absl::conjunction< + absl::negation<std::is_same<T, U> >, + std::is_constructible<T, const U&>, + absl::negation< + optional_internal:: + is_constructible_convertible_from_optional<T, U> >, + std::is_convertible<const U&, T> >::value, + bool>::type = false> + optional(const optional<U>& rhs) { + if (rhs) { + this->construct(*rhs); + } + } + + // Converting copy constructor (explicit) + template <typename U, + typename std::enable_if< + absl::conjunction< + absl::negation<std::is_same<T, U>>, + std::is_constructible<T, const U&>, + absl::negation< + optional_internal:: + is_constructible_convertible_from_optional<T, U>>, + absl::negation<std::is_convertible<const U&, T>>>::value, + bool>::type = false> + explicit optional(const optional<U>& rhs) { + if (rhs) { + this->construct(*rhs); + } + } + + // Converting move constructor (implicit) + template <typename U, + typename std::enable_if< + absl::conjunction< + absl::negation<std::is_same<T, U> >, + std::is_constructible<T, U&&>, + absl::negation< + optional_internal:: + is_constructible_convertible_from_optional<T, U> >, + std::is_convertible<U&&, T> >::value, + bool>::type = false> + optional(optional<U>&& rhs) { + if (rhs) { + this->construct(std::move(*rhs)); + } + } + + // Converting move constructor (explicit) + template < + typename U, + typename std::enable_if< + absl::conjunction< + absl::negation<std::is_same<T, U>>, std::is_constructible<T, U&&>, + absl::negation< + optional_internal::is_constructible_convertible_from_optional< + T, U>>, + absl::negation<std::is_convertible<U&&, T>>>::value, + bool>::type = false> + explicit optional(optional<U>&& rhs) { + if (rhs) { + this->construct(std::move(*rhs)); + } + } + + // Destructor. Trivial if `T` is trivially destructible. + ~optional() = default; + + // Assignment Operators + + // Assignment from `nullopt` + // + // Example: + // + // struct S { int value; }; + // optional<S> opt = absl::nullopt; // Could also use opt = { }; + optional& operator=(nullopt_t) noexcept { + this->destruct(); + return *this; + } + + // Copy assignment operator, standard semantics + optional& operator=(const optional& src) = default; + + // Move assignment operator, standard semantics + optional& operator=(optional&& src) = default; + + // Value assignment operators + template < + typename U = T, + typename = typename std::enable_if<absl::conjunction< + absl::negation< + std::is_same<optional<T>, typename std::decay<U>::type>>, + absl::negation< + absl::conjunction<std::is_scalar<T>, + std::is_same<T, typename std::decay<U>::type>>>, + std::is_constructible<T, U>, std::is_assignable<T&, U>>::value>::type> + optional& operator=(U&& v) { + this->assign(std::forward<U>(v)); + return *this; + } + + template < + typename U, + typename = typename std::enable_if<absl::conjunction< + absl::negation<std::is_same<T, U>>, + std::is_constructible<T, const U&>, std::is_assignable<T&, const U&>, + absl::negation< + optional_internal:: + is_constructible_convertible_assignable_from_optional< + T, U>>>::value>::type> + optional& operator=(const optional<U>& rhs) { + if (rhs) { + this->assign(*rhs); + } else { + this->destruct(); + } + return *this; + } + + template <typename U, + typename = typename std::enable_if<absl::conjunction< + absl::negation<std::is_same<T, U>>, std::is_constructible<T, U>, + std::is_assignable<T&, U>, + absl::negation< + optional_internal:: + is_constructible_convertible_assignable_from_optional< + T, U>>>::value>::type> + optional& operator=(optional<U>&& rhs) { + if (rhs) { + this->assign(std::move(*rhs)); + } else { + this->destruct(); + } + return *this; + } + + // Modifiers + + // optional::reset() + // + // Destroys the inner `T` value of an `absl::optional` if one is present. + void reset() noexcept { this->destruct(); } + + // optional::emplace() + // + // (Re)constructs the underlying `T` in-place with the given forwarded + // arguments. + // + // Example: + // + // optional<Foo> opt; + // opt.emplace(arg1,arg2,arg3); // Constructs Foo(arg1,arg2,arg3) + // + // If the optional is non-empty, and the `args` refer to subobjects of the + // current object, then behaviour is undefined, because the current object + // will be destructed before the new object is constructed with `args`. + template <typename... Args, + typename = typename std::enable_if< + std::is_constructible<T, Args&&...>::value>::type> + T& emplace(Args&&... args) { + this->destruct(); + this->construct(std::forward<Args>(args)...); + return reference(); + } + + // Emplace reconstruction overload for an initializer list and the given + // forwarded arguments. + // + // Example: + // + // struct Foo { + // Foo(std::initializer_list<int>); + // }; + // + // optional<Foo> opt; + // opt.emplace({1,2,3}); // Constructs Foo({1,2,3}) + template <typename U, typename... Args, + typename = typename std::enable_if<std::is_constructible< + T, std::initializer_list<U>&, Args&&...>::value>::type> + T& emplace(std::initializer_list<U> il, Args&&... args) { + this->destruct(); + this->construct(il, std::forward<Args>(args)...); + return reference(); + } + + // Swaps + + // Swap, standard semantics + void swap(optional& rhs) noexcept( + std::is_nothrow_move_constructible<T>::value&& + std::is_trivial<T>::value) { + if (*this) { + if (rhs) { + using std::swap; + swap(**this, *rhs); + } else { + rhs.construct(std::move(**this)); + this->destruct(); + } + } else { + if (rhs) { + this->construct(std::move(*rhs)); + rhs.destruct(); + } else { + // No effect (swap(disengaged, disengaged)). + } + } + } + + // Observers + + // optional::operator->() + // + // Accesses the underlying `T` value's member `m` of an `optional`. If the + // `optional` is empty, behavior is undefined. + constexpr const T* operator->() const { return this->pointer(); } + T* operator->() { + assert(this->engaged_); + return this->pointer(); + } + + // optional::operator*() + // + // Accesses the underlying `T `value of an `optional`. If the `optional` is + // empty, behavior is undefined. + constexpr const T& operator*() const & { return reference(); } + T& operator*() & { + assert(this->engaged_); + return reference(); + } + constexpr const T&& operator*() const && { + return absl::move(reference()); + } + T&& operator*() && { + assert(this->engaged_); + return std::move(reference()); + } + + // optional::operator bool() + // + // Returns false if and only if the `optional` is empty. + // + // if (opt) { + // // do something with opt.value(); + // } else { + // // opt is empty. + // } + // + constexpr explicit operator bool() const noexcept { return this->engaged_; } + + // optional::has_value() + // + // Determines whether the `optional` contains a value. Returns `false` if and + // only if `*this` is empty. + constexpr bool has_value() const noexcept { return this->engaged_; } + + // optional::value() + // + // Returns a reference to an `optional`s underlying value. The constness + // and lvalue/rvalue-ness of the `optional` is preserved to the view of + // the `T` sub-object. Throws `absl::bad_optional_access` when the `optional` + // is empty. + constexpr const T& value() const & { + return static_cast<bool>(*this) + ? reference() + : (optional_internal::throw_bad_optional_access(), reference()); + } + T& value() & { + return static_cast<bool>(*this) + ? reference() + : (optional_internal::throw_bad_optional_access(), reference()); + } + T&& value() && { // NOLINT(build/c++11) + return std::move( + static_cast<bool>(*this) + ? reference() + : (optional_internal::throw_bad_optional_access(), reference())); + } + constexpr const T&& value() const && { // NOLINT(build/c++11) + return absl::move( + static_cast<bool>(*this) + ? reference() + : (optional_internal::throw_bad_optional_access(), reference())); + } + + // optional::value_or() + // + // Returns either the value of `T` or a passed default `val` if the `optional` + // is empty. + template <typename U> + constexpr T value_or(U&& v) const& { + return static_cast<bool>(*this) + ? **this + : static_cast<T>(absl::forward<U>(v)); + } + template <typename U> + T value_or(U&& v) && { // NOLINT(build/c++11) + return static_cast<bool>(*this) ? std::move(**this) + : static_cast<T>(std::forward<U>(v)); + } + + private: + // Private accessors for internal storage viewed as pointer to T. + constexpr const T* pointer() const { return &this->data_; } + T* pointer() { return &this->data_; } + + // Private accessors for internal storage viewed as reference to T. + constexpr const T& reference() const { return *this->pointer(); } + T& reference() { return *(this->pointer()); } + + // T constraint checks. You can't have an optional of nullopt_t, in_place_t + // or a reference. + static_assert( + !std::is_same<nullopt_t, typename std::remove_cv<T>::type>::value, + "optional<nullopt_t> is not allowed."); + static_assert( + !std::is_same<in_place_t, typename std::remove_cv<T>::type>::value, + "optional<in_place_t> is not allowed."); + static_assert(!std::is_reference<T>::value, + "optional<reference> is not allowed."); +}; + +// Non-member functions + +// swap() +// +// Performs a swap between two `absl::optional` objects, using standard +// semantics. +// +// NOTE: we assume `is_swappable()` is always `true`. A compile error will +// result if this is not the case. +template <typename T, + typename std::enable_if<std::is_move_constructible<T>::value, + bool>::type = false> +void swap(optional<T>& a, optional<T>& b) noexcept(noexcept(a.swap(b))) { + a.swap(b); +} + +// make_optional() +// +// Creates a non-empty `optional<T>` where the type of `T` is deduced. An +// `absl::optional` can also be explicitly instantiated with +// `make_optional<T>(v)`. +// +// Note: `make_optional()` constructions may be declared `constexpr` for +// trivially copyable types `T`. Non-trivial types require copy elision +// support in C++17 for `make_optional` to support `constexpr` on such +// non-trivial types. +// +// Example: +// +// constexpr absl::optional<int> opt = absl::make_optional(1); +// static_assert(opt.value() == 1, ""); +template <typename T> +constexpr optional<typename std::decay<T>::type> make_optional(T&& v) { + return optional<typename std::decay<T>::type>(absl::forward<T>(v)); +} + +template <typename T, typename... Args> +constexpr optional<T> make_optional(Args&&... args) { + return optional<T>(in_place_t(), absl::forward<Args>(args)...); +} + +template <typename T, typename U, typename... Args> +constexpr optional<T> make_optional(std::initializer_list<U> il, + Args&&... args) { + return optional<T>(in_place_t(), il, + absl::forward<Args>(args)...); +} + +// Relational operators [optional.relops] + +// Empty optionals are considered equal to each other and less than non-empty +// optionals. Supports relations between optional<T> and optional<U>, between +// optional<T> and U, and between optional<T> and nullopt. +// +// Note: We're careful to support T having non-bool relationals. + +// Requires: The expression, e.g. "*x == *y" shall be well-formed and its result +// shall be convertible to bool. +// The C++17 (N4606) "Returns:" statements are translated into +// code in an obvious way here, and the original text retained as function docs. +// Returns: If bool(x) != bool(y), false; otherwise if bool(x) == false, true; +// otherwise *x == *y. +template <typename T, typename U> +constexpr auto operator==(const optional<T>& x, const optional<U>& y) + -> decltype(optional_internal::convertible_to_bool(*x == *y)) { + return static_cast<bool>(x) != static_cast<bool>(y) + ? false + : static_cast<bool>(x) == false ? true : *x == *y; +} + +// Returns: If bool(x) != bool(y), true; otherwise, if bool(x) == false, false; +// otherwise *x != *y. +template <typename T, typename U> +constexpr auto operator!=(const optional<T>& x, const optional<U>& y) + -> decltype(optional_internal::convertible_to_bool(*x != *y)) { + return static_cast<bool>(x) != static_cast<bool>(y) + ? true + : static_cast<bool>(x) == false ? false : *x != *y; +} +// Returns: If !y, false; otherwise, if !x, true; otherwise *x < *y. +template <typename T, typename U> +constexpr auto operator<(const optional<T>& x, const optional<U>& y) + -> decltype(optional_internal::convertible_to_bool(*x < *y)) { + return !y ? false : !x ? true : *x < *y; +} +// Returns: If !x, false; otherwise, if !y, true; otherwise *x > *y. +template <typename T, typename U> +constexpr auto operator>(const optional<T>& x, const optional<U>& y) + -> decltype(optional_internal::convertible_to_bool(*x > *y)) { + return !x ? false : !y ? true : *x > *y; +} +// Returns: If !x, true; otherwise, if !y, false; otherwise *x <= *y. +template <typename T, typename U> +constexpr auto operator<=(const optional<T>& x, const optional<U>& y) + -> decltype(optional_internal::convertible_to_bool(*x <= *y)) { + return !x ? true : !y ? false : *x <= *y; +} +// Returns: If !y, true; otherwise, if !x, false; otherwise *x >= *y. +template <typename T, typename U> +constexpr auto operator>=(const optional<T>& x, const optional<U>& y) + -> decltype(optional_internal::convertible_to_bool(*x >= *y)) { + return !y ? true : !x ? false : *x >= *y; +} + +// Comparison with nullopt [optional.nullops] +// The C++17 (N4606) "Returns:" statements are used directly here. +template <typename T> +constexpr bool operator==(const optional<T>& x, nullopt_t) noexcept { + return !x; +} +template <typename T> +constexpr bool operator==(nullopt_t, const optional<T>& x) noexcept { + return !x; +} +template <typename T> +constexpr bool operator!=(const optional<T>& x, nullopt_t) noexcept { + return static_cast<bool>(x); +} +template <typename T> +constexpr bool operator!=(nullopt_t, const optional<T>& x) noexcept { + return static_cast<bool>(x); +} +template <typename T> +constexpr bool operator<(const optional<T>&, nullopt_t) noexcept { + return false; +} +template <typename T> +constexpr bool operator<(nullopt_t, const optional<T>& x) noexcept { + return static_cast<bool>(x); +} +template <typename T> +constexpr bool operator<=(const optional<T>& x, nullopt_t) noexcept { + return !x; +} +template <typename T> +constexpr bool operator<=(nullopt_t, const optional<T>&) noexcept { + return true; +} +template <typename T> +constexpr bool operator>(const optional<T>& x, nullopt_t) noexcept { + return static_cast<bool>(x); +} +template <typename T> +constexpr bool operator>(nullopt_t, const optional<T>&) noexcept { + return false; +} +template <typename T> +constexpr bool operator>=(const optional<T>&, nullopt_t) noexcept { + return true; +} +template <typename T> +constexpr bool operator>=(nullopt_t, const optional<T>& x) noexcept { + return !x; +} + +// Comparison with T [optional.comp_with_t] + +// Requires: The expression, e.g. "*x == v" shall be well-formed and its result +// shall be convertible to bool. +// The C++17 (N4606) "Equivalent to:" statements are used directly here. +template <typename T, typename U> +constexpr auto operator==(const optional<T>& x, const U& v) + -> decltype(optional_internal::convertible_to_bool(*x == v)) { + return static_cast<bool>(x) ? *x == v : false; +} +template <typename T, typename U> +constexpr auto operator==(const U& v, const optional<T>& x) + -> decltype(optional_internal::convertible_to_bool(v == *x)) { + return static_cast<bool>(x) ? v == *x : false; +} +template <typename T, typename U> +constexpr auto operator!=(const optional<T>& x, const U& v) + -> decltype(optional_internal::convertible_to_bool(*x != v)) { + return static_cast<bool>(x) ? *x != v : true; +} +template <typename T, typename U> +constexpr auto operator!=(const U& v, const optional<T>& x) + -> decltype(optional_internal::convertible_to_bool(v != *x)) { + return static_cast<bool>(x) ? v != *x : true; +} +template <typename T, typename U> +constexpr auto operator<(const optional<T>& x, const U& v) + -> decltype(optional_internal::convertible_to_bool(*x < v)) { + return static_cast<bool>(x) ? *x < v : true; +} +template <typename T, typename U> +constexpr auto operator<(const U& v, const optional<T>& x) + -> decltype(optional_internal::convertible_to_bool(v < *x)) { + return static_cast<bool>(x) ? v < *x : false; +} +template <typename T, typename U> +constexpr auto operator<=(const optional<T>& x, const U& v) + -> decltype(optional_internal::convertible_to_bool(*x <= v)) { + return static_cast<bool>(x) ? *x <= v : true; +} +template <typename T, typename U> +constexpr auto operator<=(const U& v, const optional<T>& x) + -> decltype(optional_internal::convertible_to_bool(v <= *x)) { + return static_cast<bool>(x) ? v <= *x : false; +} +template <typename T, typename U> +constexpr auto operator>(const optional<T>& x, const U& v) + -> decltype(optional_internal::convertible_to_bool(*x > v)) { + return static_cast<bool>(x) ? *x > v : false; +} +template <typename T, typename U> +constexpr auto operator>(const U& v, const optional<T>& x) + -> decltype(optional_internal::convertible_to_bool(v > *x)) { + return static_cast<bool>(x) ? v > *x : true; +} +template <typename T, typename U> +constexpr auto operator>=(const optional<T>& x, const U& v) + -> decltype(optional_internal::convertible_to_bool(*x >= v)) { + return static_cast<bool>(x) ? *x >= v : false; +} +template <typename T, typename U> +constexpr auto operator>=(const U& v, const optional<T>& x) + -> decltype(optional_internal::convertible_to_bool(v >= *x)) { + return static_cast<bool>(x) ? v >= *x : true; +} + +} // namespace absl + +namespace std { + +// std::hash specialization for absl::optional. +template <typename T> +struct hash<absl::optional<T>> { + size_t operator()(const absl::optional<T>& opt) const { + if (opt) { + return hash<T>()(*opt); + } else { + return static_cast<size_t>(0x297814aaad196e6dULL); + } + } +}; + +} // namespace std + +#undef ABSL_OPTIONAL_USE_INHERITING_CONSTRUCTORS +#undef ABSL_MSVC_CONSTEXPR_BUG_IN_UNION_LIKE_CLASS + +#endif // ABSL_HAVE_STD_OPTIONAL + +#endif // ABSL_TYPES_OPTIONAL_H_ |