diff options
Diffstat (limited to 'absl/types/internal/optional.h')
| -rw-r--r-- | absl/types/internal/optional.h | 396 |
1 files changed, 396 insertions, 0 deletions
diff --git a/absl/types/internal/optional.h b/absl/types/internal/optional.h new file mode 100644 index 00000000..3c8e7cca --- /dev/null +++ b/absl/types/internal/optional.h @@ -0,0 +1,396 @@ +// 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" + +// 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 { +inline namespace lts_2019_08_08 { + +// 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>; +#ifdef 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: +#ifdef 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: +#ifdef 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 +} // inline namespace lts_2019_08_08 +} // namespace absl + +#undef ABSL_OPTIONAL_USE_INHERITING_CONSTRUCTORS + +#endif // ABSL_TYPES_INTERNAL_OPTIONAL_H_ |