diff options
Diffstat (limited to 'absl/types/optional.h')
-rw-r--r-- | absl/types/optional.h | 454 |
1 files changed, 42 insertions, 412 deletions
diff --git a/absl/types/optional.h b/absl/types/optional.h index 1ca8dec6..6614d7bd 100644 --- a/absl/types/optional.h +++ b/absl/types/optional.h @@ -4,7 +4,7 @@ // 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 +// 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, @@ -35,21 +35,21 @@ #ifndef ABSL_TYPES_OPTIONAL_H_ #define ABSL_TYPES_OPTIONAL_H_ -#include "absl/base/config.h" +#include "absl/base/config.h" // TODO(calabrese) IWYU removal? #include "absl/utility/utility.h" #ifdef ABSL_HAVE_STD_OPTIONAL -#include <optional> +#include <optional> // IWYU pragma: export namespace absl { -inline namespace lts_2018_12_18 { +inline namespace lts_2019_08_08 { using std::bad_optional_access; using std::optional; using std::make_optional; using std::nullopt_t; using std::nullopt; -} // inline namespace lts_2018_12_18 +} // inline namespace lts_2019_08_08 } // namespace absl #else // ABSL_HAVE_STD_OPTIONAL @@ -57,45 +57,33 @@ using std::nullopt; #include <cassert> #include <functional> #include <initializer_list> -#include <new> #include <type_traits> #include <utility> #include "absl/base/attributes.h" -#include "absl/memory/memory.h" +#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 +namespace absl { +inline namespace lts_2019_08_08 { + +// nullopt_t // -// 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 +// 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 {} +}; -namespace absl { -inline namespace lts_2018_12_18 { +// 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 @@ -117,10 +105,6 @@ inline namespace lts_2018_12_18 { // 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. // * The move constructor's `noexcept` specification is stronger, i.e. if the @@ -130,366 +114,13 @@ inline namespace lts_2018_12_18 { // 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; - -// 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 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) { - 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 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 { - 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< - optional_internal::get_ctor_copy_traits<T>()>, + optional_internal::ctor_copy_traits<T>::traits>, private optional_internal::optional_assign_base< - optional_internal::get_assign_copy_traits<T>()> { + optional_internal::assign_copy_traits<T>::traits> { using data_base = optional_internal::optional_data<T>; public: @@ -514,10 +145,11 @@ class optional : private optional_internal::optional_data<T>, // 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(absl-team): Add std::is_constructible<T, Args&&...> SFINAE. - template <typename... Args> - constexpr explicit optional(in_place_t, Args&&... args) + template <typename InPlaceT, typename... Args, + absl::enable_if_t<absl::conjunction< + std::is_same<InPlaceT, in_place_t>, + std::is_constructible<T, Args&&...> >::value>* = nullptr> + constexpr explicit optional(InPlaceT, Args&&... args) : data_base(in_place_t(), absl::forward<Args>(args)...) {} // Constructs a non-empty `optional` direct-initialized value of type `T` from @@ -753,11 +385,10 @@ class optional : private optional_internal::optional_data<T>, // Swap, standard semantics void swap(optional& rhs) noexcept( std::is_nothrow_move_constructible<T>::value&& - std::is_trivial<T>::value) { + type_traits_internal::IsNothrowSwappable<T>::value) { if (*this) { if (rhs) { - using std::swap; - swap(**this, *rhs); + type_traits_internal::Swap(**this, *rhs); } else { rhs.construct(std::move(**this)); this->destruct(); @@ -793,7 +424,9 @@ class optional : private optional_internal::optional_data<T>, // // Accesses the underlying `T` value of an `optional`. If the `optional` is // empty, behavior is undefined. - constexpr const T& operator*() const & { return reference(); } + constexpr const T& operator*() const& { + return ABSL_ASSERT(this->engaged_), reference(); + } T& operator*() & { assert(this->engaged_); return reference(); @@ -869,7 +502,7 @@ class optional : private optional_internal::optional_data<T>, template <typename U> constexpr T value_or(U&& v) const& { static_assert(std::is_copy_constructible<value_type>::value, - "optional<T>::value_or: T must by copy constructible"); + "optional<T>::value_or: T must be copy constructible"); static_assert(std::is_convertible<U&&, value_type>::value, "optional<T>::value_or: U must be convertible to T"); return static_cast<bool>(*this) @@ -879,7 +512,7 @@ class optional : private optional_internal::optional_data<T>, template <typename U> T value_or(U&& v) && { // NOLINT(build/c++11) static_assert(std::is_move_constructible<value_type>::value, - "optional<T>::value_or: T must by copy constructible"); + "optional<T>::value_or: T must be move constructible"); static_assert(std::is_convertible<U&&, value_type>::value, "optional<T>::value_or: U must be convertible to T"); return static_cast<bool>(*this) ? std::move(**this) @@ -909,12 +542,10 @@ class optional : private optional_internal::optional_data<T>, // // 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> +template <typename T, typename std::enable_if< + std::is_move_constructible<T>::value && + type_traits_internal::IsSwappable<T>::value, + bool>::type = false> void swap(optional<T>& a, optional<T>& b) noexcept(noexcept(a.swap(b))) { a.swap(b); } @@ -1126,7 +757,7 @@ constexpr auto operator>=(const U& v, const optional<T>& x) return static_cast<bool>(x) ? static_cast<bool>(v >= *x) : true; } -} // inline namespace lts_2018_12_18 +} // inline namespace lts_2019_08_08 } // namespace absl namespace std { @@ -1138,7 +769,6 @@ struct hash<absl::optional<T> > } // namespace std -#undef ABSL_OPTIONAL_USE_INHERITING_CONSTRUCTORS #undef ABSL_MSVC_CONSTEXPR_BUG_IN_UNION_LIKE_CLASS #endif // ABSL_HAVE_STD_OPTIONAL |