// <optional> -*- C++ -*- // Copyright (C) 2013-2020 Free Software Foundation, Inc. // // This file is part of the GNU ISO C++ Library. This library is free // software; you can redistribute it and/or modify it under the // terms of the GNU General Public License as published by the // Free Software Foundation; either version 3, or (at your option) // any later version. // This library is distributed in the hope that it will be useful, // but WITHOUT ANY WARRANTY; without even the implied warranty of // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the // GNU General Public License for more details. // Under Section 7 of GPL version 3, you are granted additional // permissions described in the GCC Runtime Library Exception, version // 3.1, as published by the Free Software Foundation. // You should have received a copy of the GNU General Public License and // a copy of the GCC Runtime Library Exception along with this program; // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see // <http://www.gnu.org/licenses/>. /** @file experimental/optional * This is a TS C++ Library header. * @ingroup libfund-ts */ #ifndef _GLIBCXX_EXPERIMENTAL_OPTIONAL #define _GLIBCXX_EXPERIMENTAL_OPTIONAL 1 #if __cplusplus >= 201402L #include <utility> #include <type_traits> #include <stdexcept> #include <new> #include <initializer_list> #include <bits/functexcept.h> #include <bits/functional_hash.h> #include <bits/enable_special_members.h> #include <experimental/bits/lfts_config.h> namespace std _GLIBCXX_VISIBILITY(default) { _GLIBCXX_BEGIN_NAMESPACE_VERSION namespace experimental { inline namespace fundamentals_v1 { /** * @defgroup optional Optional values * @ingroup libfund-ts * * Class template for optional values and surrounding facilities, as * described in n3793 "A proposal to add a utility class to represent * optional objects (Revision 5)". * * @{ */ #define __cpp_lib_experimental_optional 201411 // All subsequent [X.Y.n] references are against n3793. // [X.Y.4] template<typename _Tp> class optional; // [X.Y.5] /// Tag type for in-place construction. struct in_place_t { }; /// Tag for in-place construction. constexpr in_place_t in_place { }; // [X.Y.6] /// Tag type to disengage optional objects. struct nullopt_t { // Do not user-declare default constructor at all for // optional_value = {} syntax to work. // nullopt_t() = delete; // Used for constructing nullopt. enum class _Construct { _Token }; // Must be constexpr for nullopt_t to be literal. explicit constexpr nullopt_t(_Construct) { } }; // [X.Y.6] /// Tag to disengage optional objects. constexpr nullopt_t nullopt { nullopt_t::_Construct::_Token }; // [X.Y.7] /** * @brief Exception class thrown when a disengaged optional object is * dereferenced. * @ingroup exceptions */ class bad_optional_access : public logic_error { public: bad_optional_access() : logic_error("bad optional access") { } // XXX This constructor is non-standard. Should not be inline explicit bad_optional_access(const char* __arg) : logic_error(__arg) { } virtual ~bad_optional_access() noexcept = default; }; /// @cond undocumented void __throw_bad_optional_access(const char*) __attribute__((__noreturn__)); // XXX Does not belong here. inline void __throw_bad_optional_access(const char* __s) { _GLIBCXX_THROW_OR_ABORT(bad_optional_access(__s)); } /** * @brief Class template that holds the necessary state for @ref optional * and that has the responsibility for construction and the special members. * * Such a separate base class template is necessary in order to * conditionally enable the special members (e.g. copy/move constructors). * Note that this means that @ref _Optional_base implements the * functionality for copy and move assignment, but not for converting * assignment. * * @see optional, _Enable_special_members */ template<typename _Tp, bool _ShouldProvideDestructor = !is_trivially_destructible<_Tp>::value> class _Optional_base { private: // Remove const to avoid prohibition of reusing object storage for // const-qualified types in [3.8/9]. This is strictly internal // and even optional itself is oblivious to it. using _Stored_type = remove_const_t<_Tp>; public: // [X.Y.4.1] Constructors. // Constructors for disengaged optionals. constexpr _Optional_base() noexcept : _M_empty{} { } constexpr _Optional_base(nullopt_t) noexcept : _Optional_base{} { } // Constructors for engaged optionals. template<typename... _Args> constexpr explicit _Optional_base(in_place_t, _Args&&... __args) : _M_payload(std::forward<_Args>(__args)...), _M_engaged(true) { } template<typename _Up, typename... _Args, enable_if_t<is_constructible<_Tp, initializer_list<_Up>&, _Args&&...>::value, int>...> constexpr explicit _Optional_base(in_place_t, initializer_list<_Up> __il, _Args&&... __args) : _M_payload(__il, std::forward<_Args>(__args)...), _M_engaged(true) { } // Copy and move constructors. _Optional_base(const _Optional_base& __other) { if (__other._M_engaged) this->_M_construct(__other._M_get()); } _Optional_base(_Optional_base&& __other) noexcept(is_nothrow_move_constructible<_Tp>()) { if (__other._M_engaged) this->_M_construct(std::move(__other._M_get())); } // [X.Y.4.3] (partly) Assignment. _Optional_base& operator=(const _Optional_base& __other) { if (this->_M_engaged && __other._M_engaged) this->_M_get() = __other._M_get(); else { if (__other._M_engaged) this->_M_construct(__other._M_get()); else this->_M_reset(); } return *this; } _Optional_base& operator=(_Optional_base&& __other) noexcept(__and_<is_nothrow_move_constructible<_Tp>, is_nothrow_move_assignable<_Tp>>()) { if (this->_M_engaged && __other._M_engaged) this->_M_get() = std::move(__other._M_get()); else { if (__other._M_engaged) this->_M_construct(std::move(__other._M_get())); else this->_M_reset(); } return *this; } // [X.Y.4.2] Destructor. ~_Optional_base() { if (this->_M_engaged) this->_M_payload.~_Stored_type(); } // The following functionality is also needed by optional, hence the // protected accessibility. protected: constexpr bool _M_is_engaged() const noexcept { return this->_M_engaged; } // The _M_get operations have _M_engaged as a precondition. constexpr _Tp& _M_get() noexcept { return _M_payload; } constexpr const _Tp& _M_get() const noexcept { return _M_payload; } // The _M_construct operation has !_M_engaged as a precondition // while _M_destruct has _M_engaged as a precondition. template<typename... _Args> void _M_construct(_Args&&... __args) noexcept(is_nothrow_constructible<_Stored_type, _Args...>()) { ::new (std::__addressof(this->_M_payload)) _Stored_type(std::forward<_Args>(__args)...); this->_M_engaged = true; } void _M_destruct() { this->_M_engaged = false; this->_M_payload.~_Stored_type(); } // _M_reset is a 'safe' operation with no precondition. void _M_reset() { if (this->_M_engaged) this->_M_destruct(); } private: struct _Empty_byte { }; union { _Empty_byte _M_empty; _Stored_type _M_payload; }; bool _M_engaged = false; }; /// Partial specialization that is exactly identical to the primary template /// save for not providing a destructor, to fulfill triviality requirements. template<typename _Tp> class _Optional_base<_Tp, false> { private: using _Stored_type = remove_const_t<_Tp>; public: constexpr _Optional_base() noexcept : _M_empty{} { } constexpr _Optional_base(nullopt_t) noexcept : _Optional_base{} { } template<typename... _Args> constexpr explicit _Optional_base(in_place_t, _Args&&... __args) : _M_payload(std::forward<_Args>(__args)...), _M_engaged(true) { } template<typename _Up, typename... _Args, enable_if_t<is_constructible<_Tp, initializer_list<_Up>&, _Args&&...>::value, int>...> constexpr explicit _Optional_base(in_place_t, initializer_list<_Up> __il, _Args&&... __args) : _M_payload(__il, std::forward<_Args>(__args)...), _M_engaged(true) { } _Optional_base(const _Optional_base& __other) { if (__other._M_engaged) this->_M_construct(__other._M_get()); } _Optional_base(_Optional_base&& __other) noexcept(is_nothrow_move_constructible<_Tp>()) { if (__other._M_engaged) this->_M_construct(std::move(__other._M_get())); } _Optional_base& operator=(const _Optional_base& __other) { if (this->_M_engaged && __other._M_engaged) this->_M_get() = __other._M_get(); else { if (__other._M_engaged) this->_M_construct(__other._M_get()); else this->_M_reset(); } return *this; } _Optional_base& operator=(_Optional_base&& __other) noexcept(__and_<is_nothrow_move_constructible<_Tp>, is_nothrow_move_assignable<_Tp>>()) { if (this->_M_engaged && __other._M_engaged) this->_M_get() = std::move(__other._M_get()); else { if (__other._M_engaged) this->_M_construct(std::move(__other._M_get())); else this->_M_reset(); } return *this; } // Sole difference // ~_Optional_base() noexcept = default; protected: constexpr bool _M_is_engaged() const noexcept { return this->_M_engaged; } _Tp& _M_get() noexcept { return _M_payload; } constexpr const _Tp& _M_get() const noexcept { return _M_payload; } template<typename... _Args> void _M_construct(_Args&&... __args) noexcept(is_nothrow_constructible<_Stored_type, _Args...>()) { ::new (std::__addressof(this->_M_payload)) _Stored_type(std::forward<_Args>(__args)...); this->_M_engaged = true; } void _M_destruct() { this->_M_engaged = false; this->_M_payload.~_Stored_type(); } void _M_reset() { if (this->_M_engaged) this->_M_destruct(); } private: struct _Empty_byte { }; union { _Empty_byte _M_empty; _Stored_type _M_payload; }; bool _M_engaged = false; }; template<typename _Tp, typename _Up> using __converts_from_optional = __or_<is_constructible<_Tp, const optional<_Up>&>, is_constructible<_Tp, optional<_Up>&>, is_constructible<_Tp, const optional<_Up>&&>, is_constructible<_Tp, optional<_Up>&&>, is_convertible<const optional<_Up>&, _Tp>, is_convertible<optional<_Up>&, _Tp>, is_convertible<const optional<_Up>&&, _Tp>, is_convertible<optional<_Up>&&, _Tp>>; template<typename _Tp, typename _Up> using __assigns_from_optional = __or_<is_assignable<_Tp&, const optional<_Up>&>, is_assignable<_Tp&, optional<_Up>&>, is_assignable<_Tp&, const optional<_Up>&&>, is_assignable<_Tp&, optional<_Up>&&>>; /// @endcond /** * @brief Class template for optional values. */ template<typename _Tp> class optional : private _Optional_base<_Tp>, private _Enable_copy_move< // Copy constructor. is_copy_constructible<_Tp>::value, // Copy assignment. __and_<is_copy_constructible<_Tp>, is_copy_assignable<_Tp>>::value, // Move constructor. is_move_constructible<_Tp>::value, // Move assignment. __and_<is_move_constructible<_Tp>, is_move_assignable<_Tp>>::value, // Unique tag type. optional<_Tp>> { static_assert(__and_<__not_<is_same<remove_cv_t<_Tp>, nullopt_t>>, __not_<is_same<remove_cv_t<_Tp>, in_place_t>>, __not_<is_reference<_Tp>>>(), "Invalid instantiation of optional<T>"); private: using _Base = _Optional_base<_Tp>; public: using value_type = _Tp; // _Optional_base has the responsibility for construction. using _Base::_Base; constexpr optional() = default; // Converting constructors for engaged optionals. template <typename _Up = _Tp, enable_if_t<__and_< __not_<is_same<optional<_Tp>, decay_t<_Up>>>, is_constructible<_Tp, _Up&&>, is_convertible<_Up&&, _Tp> >::value, bool> = true> constexpr optional(_Up&& __t) : _Base(in_place, std::forward<_Up>(__t)) { } template <typename _Up = _Tp, enable_if_t<__and_< __not_<is_same<optional<_Tp>, decay_t<_Up>>>, is_constructible<_Tp, _Up&&>, __not_<is_convertible<_Up&&, _Tp>> >::value, bool> = false> explicit constexpr optional(_Up&& __t) : _Base(in_place, std::forward<_Up>(__t)) { } template <typename _Up, enable_if_t<__and_< __not_<is_same<_Tp, _Up>>, is_constructible<_Tp, const _Up&>, is_convertible<const _Up&, _Tp>, __not_<__converts_from_optional<_Tp, _Up>> >::value, bool> = true> constexpr optional(const optional<_Up>& __t) { if (__t) emplace(*__t); } template <typename _Up, enable_if_t<__and_< __not_<is_same<_Tp, _Up>>, is_constructible<_Tp, const _Up&>, __not_<is_convertible<const _Up&, _Tp>>, __not_<__converts_from_optional<_Tp, _Up>> >::value, bool> = false> explicit constexpr optional(const optional<_Up>& __t) { if (__t) emplace(*__t); } template <typename _Up, enable_if_t<__and_< __not_<is_same<_Tp, _Up>>, is_constructible<_Tp, _Up&&>, is_convertible<_Up&&, _Tp>, __not_<__converts_from_optional<_Tp, _Up>> >::value, bool> = true> constexpr optional(optional<_Up>&& __t) { if (__t) emplace(std::move(*__t)); } template <typename _Up, enable_if_t<__and_< __not_<is_same<_Tp, _Up>>, is_constructible<_Tp, _Up&&>, __not_<is_convertible<_Up&&, _Tp>>, __not_<__converts_from_optional<_Tp, _Up>> >::value, bool> = false> explicit constexpr optional(optional<_Up>&& __t) { if (__t) emplace(std::move(*__t)); } // [X.Y.4.3] (partly) Assignment. optional& operator=(nullopt_t) noexcept { this->_M_reset(); return *this; } template<typename _Up = _Tp> enable_if_t<__and_< __not_<is_same<optional<_Tp>, decay_t<_Up>>>, is_constructible<_Tp, _Up>, __not_<__and_<is_scalar<_Tp>, is_same<_Tp, decay_t<_Up>>>>, is_assignable<_Tp&, _Up>>::value, optional&> operator=(_Up&& __u) { if (this->_M_is_engaged()) this->_M_get() = std::forward<_Up>(__u); else this->_M_construct(std::forward<_Up>(__u)); return *this; } template<typename _Up> enable_if_t<__and_< __not_<is_same<_Tp, _Up>>, is_constructible<_Tp, const _Up&>, is_assignable<_Tp&, _Up>, __not_<__converts_from_optional<_Tp, _Up>>, __not_<__assigns_from_optional<_Tp, _Up>> >::value, optional&> operator=(const optional<_Up>& __u) { if (__u) { if (this->_M_is_engaged()) this->_M_get() = *__u; else this->_M_construct(*__u); } else { this->_M_reset(); } return *this; } template<typename _Up> enable_if_t<__and_< __not_<is_same<_Tp, _Up>>, is_constructible<_Tp, _Up>, is_assignable<_Tp&, _Up>, __not_<__converts_from_optional<_Tp, _Up>>, __not_<__assigns_from_optional<_Tp, _Up>> >::value, optional&> operator=(optional<_Up>&& __u) { if (__u) { if (this->_M_is_engaged()) this->_M_get() = std::move(*__u); else this->_M_construct(std::move(*__u)); } else { this->_M_reset(); } return *this; } template<typename... _Args> enable_if_t<is_constructible<_Tp, _Args&&...>::value> emplace(_Args&&... __args) { this->_M_reset(); this->_M_construct(std::forward<_Args>(__args)...); } template<typename _Up, typename... _Args> enable_if_t<is_constructible<_Tp, initializer_list<_Up>&, _Args&&...>::value> emplace(initializer_list<_Up> __il, _Args&&... __args) { this->_M_reset(); this->_M_construct(__il, std::forward<_Args>(__args)...); } // [X.Y.4.2] Destructor is implicit, implemented in _Optional_base. // [X.Y.4.4] Swap. void swap(optional& __other) noexcept(is_nothrow_move_constructible<_Tp>() && __is_nothrow_swappable<_Tp>::value) { using std::swap; if (this->_M_is_engaged() && __other._M_is_engaged()) swap(this->_M_get(), __other._M_get()); else if (this->_M_is_engaged()) { __other._M_construct(std::move(this->_M_get())); this->_M_destruct(); } else if (__other._M_is_engaged()) { this->_M_construct(std::move(__other._M_get())); __other._M_destruct(); } } // [X.Y.4.5] Observers. constexpr const _Tp* operator->() const { return std::__addressof(this->_M_get()); } _Tp* operator->() { return std::__addressof(this->_M_get()); } constexpr const _Tp& operator*() const& { return this->_M_get(); } constexpr _Tp& operator*()& { return this->_M_get(); } constexpr _Tp&& operator*()&& { return std::move(this->_M_get()); } constexpr const _Tp&& operator*() const&& { return std::move(this->_M_get()); } constexpr explicit operator bool() const noexcept { return this->_M_is_engaged(); } constexpr const _Tp& value() const& { return this->_M_is_engaged() ? this->_M_get() : (__throw_bad_optional_access("Attempt to access value of a " "disengaged optional object"), this->_M_get()); } constexpr _Tp& value()& { return this->_M_is_engaged() ? this->_M_get() : (__throw_bad_optional_access("Attempt to access value of a " "disengaged optional object"), this->_M_get()); } constexpr _Tp&& value()&& { return this->_M_is_engaged() ? std::move(this->_M_get()) : (__throw_bad_optional_access("Attempt to access value of a " "disengaged optional object"), std::move(this->_M_get())); } constexpr const _Tp&& value() const&& { return this->_M_is_engaged() ? std::move(this->_M_get()) : (__throw_bad_optional_access("Attempt to access value of a " "disengaged optional object"), std::move(this->_M_get())); } template<typename _Up> constexpr _Tp value_or(_Up&& __u) const& { static_assert(__and_<is_copy_constructible<_Tp>, is_convertible<_Up&&, _Tp>>(), "Cannot return value"); return this->_M_is_engaged() ? this->_M_get() : static_cast<_Tp>(std::forward<_Up>(__u)); } template<typename _Up> _Tp value_or(_Up&& __u) && { static_assert(__and_<is_move_constructible<_Tp>, is_convertible<_Up&&, _Tp>>(), "Cannot return value" ); return this->_M_is_engaged() ? std::move(this->_M_get()) : static_cast<_Tp>(std::forward<_Up>(__u)); } }; /// @relates experimental::optional @{ // [X.Y.8] Comparisons between optional values. template<typename _Tp> constexpr bool operator==(const optional<_Tp>& __lhs, const optional<_Tp>& __rhs) { return static_cast<bool>(__lhs) == static_cast<bool>(__rhs) && (!__lhs || *__lhs == *__rhs); } template<typename _Tp> constexpr bool operator!=(const optional<_Tp>& __lhs, const optional<_Tp>& __rhs) { return !(__lhs == __rhs); } template<typename _Tp> constexpr bool operator<(const optional<_Tp>& __lhs, const optional<_Tp>& __rhs) { return static_cast<bool>(__rhs) && (!__lhs || *__lhs < *__rhs); } template<typename _Tp> constexpr bool operator>(const optional<_Tp>& __lhs, const optional<_Tp>& __rhs) { return __rhs < __lhs; } template<typename _Tp> constexpr bool operator<=(const optional<_Tp>& __lhs, const optional<_Tp>& __rhs) { return !(__rhs < __lhs); } template<typename _Tp> constexpr bool operator>=(const optional<_Tp>& __lhs, const optional<_Tp>& __rhs) { return !(__lhs < __rhs); } // [X.Y.9] Comparisons with nullopt. template<typename _Tp> constexpr bool operator==(const optional<_Tp>& __lhs, nullopt_t) noexcept { return !__lhs; } template<typename _Tp> constexpr bool operator==(nullopt_t, const optional<_Tp>& __rhs) noexcept { return !__rhs; } template<typename _Tp> constexpr bool operator!=(const optional<_Tp>& __lhs, nullopt_t) noexcept { return static_cast<bool>(__lhs); } template<typename _Tp> constexpr bool operator!=(nullopt_t, const optional<_Tp>& __rhs) noexcept { return static_cast<bool>(__rhs); } template<typename _Tp> constexpr bool operator<(const optional<_Tp>& /* __lhs */, nullopt_t) noexcept { return false; } template<typename _Tp> constexpr bool operator<(nullopt_t, const optional<_Tp>& __rhs) noexcept { return static_cast<bool>(__rhs); } template<typename _Tp> constexpr bool operator>(const optional<_Tp>& __lhs, nullopt_t) noexcept { return static_cast<bool>(__lhs); } template<typename _Tp> constexpr bool operator>(nullopt_t, const optional<_Tp>& /* __rhs */) noexcept { return false; } template<typename _Tp> constexpr bool operator<=(const optional<_Tp>& __lhs, nullopt_t) noexcept { return !__lhs; } template<typename _Tp> constexpr bool operator<=(nullopt_t, const optional<_Tp>& /* __rhs */) noexcept { return true; } template<typename _Tp> constexpr bool operator>=(const optional<_Tp>& /* __lhs */, nullopt_t) noexcept { return true; } template<typename _Tp> constexpr bool operator>=(nullopt_t, const optional<_Tp>& __rhs) noexcept { return !__rhs; } // [X.Y.10] Comparisons with value type. template<typename _Tp> constexpr bool operator==(const optional<_Tp>& __lhs, const _Tp& __rhs) { return __lhs && *__lhs == __rhs; } template<typename _Tp> constexpr bool operator==(const _Tp& __lhs, const optional<_Tp>& __rhs) { return __rhs && __lhs == *__rhs; } template<typename _Tp> constexpr bool operator!=(const optional<_Tp>& __lhs, _Tp const& __rhs) { return !__lhs || !(*__lhs == __rhs); } template<typename _Tp> constexpr bool operator!=(const _Tp& __lhs, const optional<_Tp>& __rhs) { return !__rhs || !(__lhs == *__rhs); } template<typename _Tp> constexpr bool operator<(const optional<_Tp>& __lhs, const _Tp& __rhs) { return !__lhs || *__lhs < __rhs; } template<typename _Tp> constexpr bool operator<(const _Tp& __lhs, const optional<_Tp>& __rhs) { return __rhs && __lhs < *__rhs; } template<typename _Tp> constexpr bool operator>(const optional<_Tp>& __lhs, const _Tp& __rhs) { return __lhs && __rhs < *__lhs; } template<typename _Tp> constexpr bool operator>(const _Tp& __lhs, const optional<_Tp>& __rhs) { return !__rhs || *__rhs < __lhs; } template<typename _Tp> constexpr bool operator<=(const optional<_Tp>& __lhs, const _Tp& __rhs) { return !__lhs || !(__rhs < *__lhs); } template<typename _Tp> constexpr bool operator<=(const _Tp& __lhs, const optional<_Tp>& __rhs) { return __rhs && !(*__rhs < __lhs); } template<typename _Tp> constexpr bool operator>=(const optional<_Tp>& __lhs, const _Tp& __rhs) { return __lhs && !(*__lhs < __rhs); } template<typename _Tp> constexpr bool operator>=(const _Tp& __lhs, const optional<_Tp>& __rhs) { return !__rhs || !(__lhs < *__rhs); } // [X.Y.11] template<typename _Tp> inline void swap(optional<_Tp>& __lhs, optional<_Tp>& __rhs) noexcept(noexcept(__lhs.swap(__rhs))) { __lhs.swap(__rhs); } template<typename _Tp> constexpr optional<decay_t<_Tp>> make_optional(_Tp&& __t) { return optional<decay_t<_Tp>> { std::forward<_Tp>(__t) }; } // @} relates experimental::optional // @} group optional } // namespace fundamentals_v1 } // namespace experimental // [X.Y.12] /// std::hash partial specialization for experimental::optional /// @relates experimental::optional template<typename _Tp> struct hash<experimental::optional<_Tp>> { using result_type = size_t; using argument_type = experimental::optional<_Tp>; size_t operator()(const experimental::optional<_Tp>& __t) const noexcept(noexcept(hash<_Tp> {}(*__t))) { // We pick an arbitrary hash for disengaged optionals which hopefully // usual values of _Tp won't typically hash to. constexpr size_t __magic_disengaged_hash = static_cast<size_t>(-3333); return __t ? hash<_Tp> {}(*__t) : __magic_disengaged_hash; } }; _GLIBCXX_END_NAMESPACE_VERSION } // namespace std #endif // C++14 #endif // _GLIBCXX_EXPERIMENTAL_OPTIONAL