diff options
Diffstat (limited to 'absl/types')
| -rw-r--r-- | absl/types/BUILD.bazel | 1 | ||||
| -rw-r--r-- | absl/types/CMakeLists.txt | 2 | ||||
| -rw-r--r-- | absl/types/internal/optional.h | 364 | ||||
| -rw-r--r-- | absl/types/optional.h | 375 |
4 files changed, 385 insertions, 357 deletions
diff --git a/absl/types/BUILD.bazel b/absl/types/BUILD.bazel index feac34b1c9f9..a25487184bc1 100644 --- a/absl/types/BUILD.bazel +++ b/absl/types/BUILD.bazel @@ -173,6 +173,7 @@ cc_test( cc_library( name = "optional", + srcs = ["internal/optional.h"], hdrs = ["optional.h"], copts = ABSL_DEFAULT_COPTS, linkopts = ABSL_DEFAULT_LINKOPTS, diff --git a/absl/types/CMakeLists.txt b/absl/types/CMakeLists.txt index 56f9fffd6f92..9da94eb56120 100644 --- a/absl/types/CMakeLists.txt +++ b/absl/types/CMakeLists.txt @@ -174,6 +174,8 @@ absl_cc_library( optional HDRS "optional.h" + SRCS + "internal/optional.h" COPTS ${ABSL_DEFAULT_COPTS} DEPS diff --git a/absl/types/internal/optional.h b/absl/types/internal/optional.h new file mode 100644 index 000000000000..562c84ef5af7 --- /dev/null +++ b/absl/types/internal/optional.h @@ -0,0 +1,364 @@ +// 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 +// +// https://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 ABSL_TYPES_INTERNAL_OPTIONAL_H_ +#define ABSL_TYPES_INTERNAL_OPTIONAL_H_ + +#include <functional> +#include <new> +#include <type_traits> +#include <utility> + +#include "absl/base/internal/inline_variable.h" +#include "absl/memory/memory.h" +#include "absl/meta/type_traits.h" +#include "absl/utility/utility.h" + +namespace absl { + +// Forward declaration +template <typename T> +class optional; + +namespace optional_internal { + +// This tag type is used as a constructor parameter type for `nullopt_t`. +struct init_t { + explicit init_t() = default; +}; + +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 unused = 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(absl-team): Add another 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 unused = 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) : optional_data_base<T>() { + 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) + : optional_data_base<T>() { + 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> +struct ctor_copy_traits { + static constexpr copy_traits traits = + 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> +struct assign_copy_traits { + static constexpr copy_traits traits = + absl::is_copy_assignable<T>::value && std::is_copy_constructible<T>::value + ? copy_traits::copyable + : absl::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); + +// Base class for std::hash<absl::optional<T>>: +// If std::hash<std::remove_const_t<T>> is enabled, it provides operator() to +// compute the hash; Otherwise, it is disabled. +// Reference N4659 23.14.15 [unord.hash]. +template <typename T, typename = size_t> +struct optional_hash_base { + optional_hash_base() = delete; + optional_hash_base(const optional_hash_base&) = delete; + optional_hash_base(optional_hash_base&&) = delete; + optional_hash_base& operator=(const optional_hash_base&) = delete; + optional_hash_base& operator=(optional_hash_base&&) = delete; +}; + +template <typename T> +struct optional_hash_base<T, decltype(std::hash<absl::remove_const_t<T> >()( + std::declval<absl::remove_const_t<T> >()))> { + using argument_type = absl::optional<T>; + using result_type = size_t; + size_t operator()(const absl::optional<T>& opt) const { + absl::type_traits_internal::AssertHashEnabled<absl::remove_const_t<T>>(); + if (opt) { + return std::hash<absl::remove_const_t<T> >()(*opt); + } else { + return static_cast<size_t>(0x297814aaad196e6dULL); + } + } +}; + +} // namespace optional_internal +} // namespace absl + +#endif // ABSL_TYPES_INTERNAL_OPTIONAL_H_ diff --git a/absl/types/optional.h b/absl/types/optional.h index 6806160dff7f..17f789847386 100644 --- a/absl/types/optional.h +++ b/absl/types/optional.h @@ -35,8 +35,7 @@ #ifndef ABSL_TYPES_OPTIONAL_H_ #define ABSL_TYPES_OPTIONAL_H_ -#include "absl/base/config.h" -#include "absl/memory/memory.h" +#include "absl/base/config.h" // TODO(calabrese) IWYU removal? #include "absl/utility/utility.h" #ifdef ABSL_HAVE_STD_OPTIONAL @@ -56,7 +55,6 @@ using std::nullopt; #include <cassert> #include <functional> #include <initializer_list> -#include <new> #include <type_traits> #include <utility> @@ -64,6 +62,7 @@ using std::nullopt; #include "absl/base/internal/inline_variable.h" #include "absl/meta/type_traits.h" #include "absl/types/bad_optional_access.h" +#include "absl/types/internal/optional.h" // ABSL_OPTIONAL_USE_INHERITING_CONSTRUCTORS // @@ -95,6 +94,22 @@ using std::nullopt; namespace absl { +// nullopt_t +// +// Class type for `absl::nullopt` used to indicate an `absl::optional<T>` type +// that does not contain a value. +struct nullopt_t { + // It must not be default-constructible to avoid ambiguity for opt = {}. + explicit constexpr nullopt_t(optional_internal::init_t) noexcept {} +}; + +// nullopt +// +// A tag constant of type `absl::nullopt_t` used to indicate an empty +// `absl::optional` in certain functions, such as construction or assignment. +ABSL_INTERNAL_INLINE_CONSTEXPR(nullopt_t, nullopt, + nullopt_t(optional_internal::init_t())); + // ----------------------------------------------------------------------------- // absl::optional // ----------------------------------------------------------------------------- @@ -124,361 +139,7 @@ namespace absl { // a) move constructors should only throw due to allocation failure and // b) if T's move constructor allocates, it uses the same allocation // function as the default allocator. -template <typename T> -class optional; - -namespace optional_internal { - -// This tag type is used as a constructor parameter type for `nullopt_t`. -struct init_t { - explicit init_t() = default; -}; - -} // namespace optional_internal - -// nullopt_t -// -// Class type for `absl::nullopt` used to indicate an `absl::optional<T>` type -// that does not contain a value. -struct nullopt_t { - // It must not be default-constructible to avoid ambiguity for opt = {}. - explicit constexpr nullopt_t(optional_internal::init_t) noexcept {} -}; - -// nullopt // -// A tag constant of type `absl::nullopt_t` used to indicate an empty -// `absl::optional` in certain functions, such as construction or assignment. -ABSL_INTERNAL_INLINE_CONSTEXPR(nullopt_t, nullopt, - nullopt_t(optional_internal::init_t())); - -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 unused = 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(absl-team): Add another 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 unused = 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) : optional_data_base<T>() { - 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) - : optional_data_base<T>() { - 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> -struct ctor_copy_traits { - static constexpr copy_traits traits = - 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> -struct assign_copy_traits { - static constexpr copy_traits traits = - absl::is_copy_assignable<T>::value && std::is_copy_constructible<T>::value - ? copy_traits::copyable - : absl::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); - -// Base class for std::hash<absl::optional<T>>: -// If std::hash<std::remove_const_t<T>> is enabled, it provides operator() to -// compute the hash; Otherwise, it is disabled. -// Reference N4659 23.14.15 [unord.hash]. -template <typename T, typename = size_t> -struct optional_hash_base { - optional_hash_base() = delete; - optional_hash_base(const optional_hash_base&) = delete; - optional_hash_base(optional_hash_base&&) = delete; - optional_hash_base& operator=(const optional_hash_base&) = delete; - optional_hash_base& operator=(optional_hash_base&&) = delete; -}; - -template <typename T> -struct optional_hash_base<T, decltype(std::hash<absl::remove_const_t<T> >()( - std::declval<absl::remove_const_t<T> >()))> { - using argument_type = absl::optional<T>; - using result_type = size_t; - size_t operator()(const absl::optional<T>& opt) const { - absl::type_traits_internal::AssertHashEnabled<absl::remove_const_t<T>>(); - if (opt) { - return std::hash<absl::remove_const_t<T> >()(*opt); - } else { - return static_cast<size_t>(0x297814aaad196e6dULL); - } - } -}; - -} // namespace optional_internal - -// ----------------------------------------------------------------------------- -// absl::optional class definition -// ----------------------------------------------------------------------------- - template <typename T> class optional : private optional_internal::optional_data<T>, private optional_internal::optional_ctor_base< |