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diff --git a/absl/types/variant.h b/absl/types/variant.h new file mode 100644 index 000000000000..52a311e37d3b --- /dev/null +++ b/absl/types/variant.h @@ -0,0 +1,838 @@ +// Copyright 2018 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. +// +// ----------------------------------------------------------------------------- +// variant.h +// ----------------------------------------------------------------------------- +// +// This header file defines an `absl::variant` type for holding a type-safe +// value of some prescribed set of types (noted as alternative types), and +// associated functions for managing variants. +// +// The `absl::variant` type is a form of type-safe union. An `absl::variant` +// should always hold a value of one of its alternative types (except in the +// "valueless by exception state" -- see below). A default-constructed +// `absl::variant` will hold the value of its first alternative type, provided +// it is default-constructable. +// +// In exceptional cases due to error, an `absl::variant` can hold no +// value (known as a "valueless by exception" state), though this is not the +// norm. +// +// As with `absl::optional`, an `absl::variant` -- when it holds a value -- +// allocates a value of that type directly within the `variant` itself; it +// cannot hold a reference, array, or the type `void`; it can, however, hold a +// pointer to externally managed memory. +// +// `absl::variant` is a C++11 compatible version of the C++17 `std::variant` +// abstraction and is designed to be a drop-in replacement for code compliant +// with C++17. + +#ifndef ABSL_TYPES_VARIANT_H_ +#define ABSL_TYPES_VARIANT_H_ + +#include "absl/base/config.h" +#include "absl/utility/utility.h" + +#ifdef ABSL_HAVE_STD_VARIANT + +#include <variant> + +namespace absl { +using std::bad_variant_access; +using std::get; +using std::get_if; +using std::holds_alternative; +using std::monostate; +using std::variant; +using std::variant_alternative; +using std::variant_alternative_t; +using std::variant_npos; +using std::variant_size; +using std::variant_size_v; +using std::visit; +} // namespace absl + +#else // ABSL_HAVE_STD_VARIANT + +#include <functional> +#include <new> +#include <type_traits> +#include <utility> + +#include "absl/base/macros.h" +#include "absl/base/port.h" +#include "absl/meta/type_traits.h" +#include "absl/types/internal/variant.h" + +namespace absl { + +// ----------------------------------------------------------------------------- +// absl::variant +// ----------------------------------------------------------------------------- +// +// An 'absl::variant` type is a form of type-safe union. An `absl::variant` -- +// except in exceptional cases -- always holds a value of one of its alternative +// types. +// +// Example: +// +// // Construct a variant that holds either an integer or a std::string and +// // assign it to a std::string. +// absl::variant<int, std::string> v = std::string("abc"); +// +// // A default-contructed variant will hold a value-initialized value of +// // the first alternative type. +// auto a = absl::variant<int, std::string>(); // Holds an int of value '0'. +// +// // variants are assignable. +// +// // copy assignment +// auto v1 = absl::variant<int, std::string>("abc"); +// auto v2 = absl::variant<int, std::string>(10); +// v2 = v1; // copy assign +// +// // move assignment +// auto v1 = absl::variant<int, std::string>("abc"); +// v1 = absl::variant<int, std::string>(10); +// +// // assignment through type conversion +// a = 128; // variant contains int +// a = "128"; // variant contains std::string +// +// An `absl::variant` holding a value of one of its alternative types `T` holds +// an allocation of `T` directly within the variant itself. An `absl::variant` +// is not allowed to allocate additional storage, such as dynamic memory, to +// allocate the contained value. The contained value shall be allocated in a +// region of the variant storage suitably aligned for all alternative types. +template <typename... Ts> +class variant; + +// swap() +// +// Swaps two `absl::variant` values. This function is equivalent to `v.swap(w)` +// where `v` and `w` are `absl::variant` types. +// +// Note that this function requires all alternative types to be both swappable +// and move-constructible, because any two variants may refer to either the same +// type (in which case, they will be swapped) or to two different types (in +// which case the values will need to be moved). +// +template <typename... Ts> +void swap(variant<Ts...>& v, variant<Ts...>& w) noexcept(noexcept(v.swap(w))) { + v.swap(w); +} + +// variant_size +// +// Returns the number of alterative types available for a given `absl::variant` +// type as a compile-time constant expression. As this is a class template, it +// is not generally useful for accessing the number of alternative types of +// any given `absl::variant` instance. +// +// Example: +// +// auto a = absl::variant<int, std::string>; +// constexpr int num_types = +// absl::variant_size<absl::variant<int, std::string>>(); +// +// // You can also use the member constant `value`. +// constexpr int num_types = +// absl::variant_size<absl::variant<int, std::string>>::value; +// +// // `absl::variant_size` is more valuable for use in generic code: +// template <typename Variant> +// constexpr bool IsVariantMultivalue() { +// return absl::variant_size<Variant>() > 1; +// } +// +// Note that the set of cv-qualified specializations of `variant_size` are +// provided to ensure that those specializations compile (especially when passed +// within template logic). +template <class T> +struct variant_size; + +template <class... Ts> +struct variant_size<variant<Ts...>> + : std::integral_constant<std::size_t, sizeof...(Ts)> {}; + +// Specialization of `variant_size` for const qualified variants. +template <class T> +struct variant_size<const T> : variant_size<T>::type {}; + +// Specialization of `variant_size` for volatile qualified variants. +template <class T> +struct variant_size<volatile T> : variant_size<T>::type {}; + +// Specialization of `variant_size` for const volatile qualified variants. +template <class T> +struct variant_size<const volatile T> : variant_size<T>::type {}; + +// variant_alternative +// +// Returns the alternative type for a given `absl::variant` at the passed +// index value as a compile-time constant expression. As this is a class +// template resulting in a type, it is not useful for access of the run-time +// value of any given `absl::variant` variable. +// +// Example: +// +// // The type of the 0th alternative is "int". +// using alternative_type_0 +// = absl::variant_alternative<0, absl::variant<int, std::string>>::type; +// +// static_assert(std::is_same<alternative_type_0, int>::value, ""); +// +// // `absl::variant_alternative` is more valuable for use in generic code: +// template <typename Variant> +// constexpr bool IsFirstElementTrivial() { +// return std::is_trivial_v<variant_alternative<0, Variant>::type>; +// } +// +// Note that the set of cv-qualified specializations of `variant_alternative` +// are provided to ensure that those specializations compile (especially when +// passed within template logic). +template <std::size_t I, class T> +struct variant_alternative; + +template <std::size_t I, class... Types> +struct variant_alternative<I, variant<Types...>> { + using type = + variant_internal::VariantAlternativeSfinaeT<I, variant<Types...>>; +}; + +// Specialization of `variant_alternative` for const qualified variants. +template <std::size_t I, class T> +struct variant_alternative<I, const T> { + using type = const typename variant_alternative<I, T>::type; +}; + +// Specialization of `variant_alternative` for volatile qualified variants. +template <std::size_t I, class T> +struct variant_alternative<I, volatile T> { + using type = volatile typename variant_alternative<I, T>::type; +}; + +// Specialization of `variant_alternative` for const volatile qualified +// variants. +template <std::size_t I, class T> +struct variant_alternative<I, const volatile T> { + using type = const volatile typename variant_alternative<I, T>::type; +}; + +// Template type alias for variant_alternative<I, T>::type. +// +// Example: +// +// using alternative_type_0 +// = absl::variant_alternative_t<0, absl::variant<int, std::string>>; +// static_assert(std::is_same<alternative_type_0, int>::value, ""); +template <std::size_t I, class T> +using variant_alternative_t = typename variant_alternative<I, T>::type; + +// holds_alternative() +// +// Checks whether the given variant currently holds a given alternative type, +// returning `true` if so. +// +// Example: +// +// absl::variant<int, std::string> bar = 42; +// if (absl::holds_alternative<int>(foo)) { +// std::cout << "The variant holds an integer"; +// } +template <class T, class... Types> +constexpr bool holds_alternative(const variant<Types...>& v) noexcept { + static_assert( + variant_internal::UnambiguousIndexOfImpl<variant<Types...>, T, + 0>::value != sizeof...(Types), + "The type T must occur exactly once in Types..."); + return v.index() == + variant_internal::UnambiguousIndexOf<variant<Types...>, T>::value; +} + +// get() +// +// Returns a reference to the value currently within a given variant, using +// either a unique alternative type amongst the variant's set of alternative +// types, or the variant's index value. Attempting to get a variant's value +// using a type that is not unique within the variant's set of alternative types +// is a compile-time error. If the index of the alternative being specified is +// different from the index of the alternative that is currently stored, throws +// `absl::bad_variant_access`. +// +// Example: +// +// auto a = absl::variant<int, std::string>; +// +// // Get the value by type (if unique). +// int i = absl::get<int>(a); +// +// auto b = absl::variant<int, int>; +// +// // Getting the value by a type that is not unique is ill-formed. +// int j = absl::get<int>(b); // Compile Error! +// +// // Getting value by index not ambiguous and allowed. +// int k = absl::get<1>(b); + +// Overload for getting a variant's lvalue by type. +template <class T, class... Types> +constexpr T& get(variant<Types...>& v) { // NOLINT + return variant_internal::VariantCoreAccess::Access< + variant_internal::IndexOf<T, Types...>::value>(v); +} + +// Overload for getting a variant's rvalue by type. +// Note: `absl::move()` is required to allow use of constexpr in C++11. +template <class T, class... Types> +constexpr T&& get(variant<Types...>&& v) { + return variant_internal::VariantCoreAccess::Access< + variant_internal::IndexOf<T, Types...>::value>(absl::move(v)); +} + +// Overload for getting a variant's const lvalue by type. +template <class T, class... Types> +constexpr const T& get(const variant<Types...>& v) { + return variant_internal::VariantCoreAccess::Access< + variant_internal::IndexOf<T, Types...>::value>(v); +} + +// Overload for getting a variant's const rvalue by type. +// Note: `absl::move()` is required to allow use of constexpr in C++11. +template <class T, class... Types> +constexpr const T&& get(const variant<Types...>&& v) { + return variant_internal::VariantCoreAccess::Access< + variant_internal::IndexOf<T, Types...>::value>(absl::move(v)); +} + +// Overload for getting a variant's lvalue by index. +template <std::size_t I, class... Types> +constexpr variant_alternative_t<I, variant<Types...>>& get( + variant<Types...>& v) { // NOLINT + return variant_internal::VariantCoreAccess::Access<I>(v); +} + +// Overload for getting a variant's rvalue by index. +// Note: `absl::move()` is required to allow use of constexpr in C++11. +template <std::size_t I, class... Types> +constexpr variant_alternative_t<I, variant<Types...>>&& get( + variant<Types...>&& v) { + return variant_internal::VariantCoreAccess::Access<I>(absl::move(v)); +} + +// Overload for getting a variant's const lvalue by index. +template <std::size_t I, class... Types> +constexpr const variant_alternative_t<I, variant<Types...>>& get( + const variant<Types...>& v) { + return variant_internal::VariantCoreAccess::Access<I>(v); +} + +// Overload for getting a variant's const rvalue by index. +// Note: `absl::move()` is required to allow use of constexpr in C++11. +template <std::size_t I, class... Types> +constexpr const variant_alternative_t<I, variant<Types...>>&& get( + const variant<Types...>&& v) { + return variant_internal::VariantCoreAccess::Access<I>(absl::move(v)); +} + +// get_if() +// +// Returns a pointer to the value currently stored within a given variant, if +// present, using either a unique alternative type amonst the variant's set of +// alternative types, or the variant's index value. If such a value does not +// exist, returns `nullptr`. +// +// As with `get`, attempting to get a variant's value using a type that is not +// unique within the variant's set of alternative types is a compile-time error. + +// Overload for getting a pointer to the value stored in the given variant by +// index. +template <std::size_t I, class... Types> +constexpr absl::add_pointer_t<variant_alternative_t<I, variant<Types...>>> +get_if(variant<Types...>* v) noexcept { + return (v != nullptr && v->index() == I) ? std::addressof(absl::get<I>(*v)) + : nullptr; +} + +// Overload for getting a pointer to the const value stored in the given +// variant by index. +template <std::size_t I, class... Types> +constexpr absl::add_pointer_t<const variant_alternative_t<I, variant<Types...>>> +get_if(const variant<Types...>* v) noexcept { + return (v != nullptr && v->index() == I) ? std::addressof(absl::get<I>(*v)) + : nullptr; +} + +// Overload for getting a pointer to the value stored in the given variant by +// type. +template <class T, class... Types> +constexpr absl::add_pointer_t<T> get_if(variant<Types...>* v) noexcept { + return absl::get_if<variant_internal::IndexOf<T, Types...>::value>(v); +} + +// Overload for getting a pointer to the const value stored in the given variant +// by type. +template <class T, class... Types> +constexpr absl::add_pointer_t<const T> get_if( + const variant<Types...>* v) noexcept { + return absl::get_if<variant_internal::IndexOf<T, Types...>::value>(v); +} + +// visit() +// +// Calls a provided functor on a given set of variants. `absl::visit()` is +// commonly used to conditionally inspect the state of a given variant (or set +// of variants). +// Requires: The expression in the Effects: element shall be a valid expression +// of the same type and value category, for all combinations of alternative +// types of all variants. Otherwise, the program is ill-formed. +// +// Example: +// +// // Define a visitor functor +// struct GetVariant { +// template<typename T> +// void operator()(const T& i) const { +// std::cout << "The variant's value is: " << i; +// } +// }; +// +// // Declare our variant, and call `absl::visit()` on it. +// std::variant<int, std::string> foo = std::string("foo"); +// GetVariant visitor; +// std::visit(visitor, foo); // Prints `The variant's value is: foo' +template <typename Visitor, typename... Variants> +variant_internal::VisitResult<Visitor, Variants...> visit(Visitor&& vis, + Variants&&... vars) { + return variant_internal::visit_indices< + variant_size<absl::decay_t<Variants>>::value...>( + variant_internal::PerformVisitation<Visitor, Variants...>{ + std::forward_as_tuple(absl::forward<Variants>(vars)...), + absl::forward<Visitor>(vis)}, + vars.index()...); +} + +// monostate +// +// The monostate class serves as a first alternative type for a variant for +// which the first variant type is otherwise not default-constructible. +struct monostate {}; + +// `absl::monostate` Relational Operators + +constexpr bool operator<(monostate, monostate) noexcept { return false; } +constexpr bool operator>(monostate, monostate) noexcept { return false; } +constexpr bool operator<=(monostate, monostate) noexcept { return true; } +constexpr bool operator>=(monostate, monostate) noexcept { return true; } +constexpr bool operator==(monostate, monostate) noexcept { return true; } +constexpr bool operator!=(monostate, monostate) noexcept { return false; } + + +//------------------------------------------------------------------------------ +// `absl::variant` Template Definition +//------------------------------------------------------------------------------ +template <typename T0, typename... Tn> +class variant<T0, Tn...> : private variant_internal::VariantBase<T0, Tn...> { + static_assert(absl::conjunction<std::is_object<T0>, std::is_object<Tn>..., + absl::negation<std::is_array<T0>>, + absl::negation<std::is_array<Tn>>..., + std::is_nothrow_destructible<T0>, + std::is_nothrow_destructible<Tn>...>::value, + "Attempted to instantiate a variant with an unsupported type."); + + friend struct variant_internal::VariantCoreAccess; + + private: + using Base = variant_internal::VariantBase<T0, Tn...>; + + public: + // Constructors + + // Constructs a variant holding a default-initialized value of the first + // alternative type. + constexpr variant() /*noexcept(see 111above)*/ = default; + + // Copy constructor, standard semantics + variant(const variant& other) = default; + + // Move constructor, standard semantics + variant(variant&& other) /*noexcept(see above)*/ = default; + + // Constructs a variant of an alternative type specified by overload + // resolution of the provided forwarding arguments through + // direct-initialization. + // + // Note: If the selected constructor is a constexpr constructor, this + // constructor shall be a constexpr constructor. + // + // NOTE: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0608r1.html + // has been voted passed the design phase in the C++ standard meeting in Mar + // 2018. It will be implemented and integrated into `absl::variant`. + template < + class T, + std::size_t I = std::enable_if< + variant_internal::IsNeitherSelfNorInPlace<variant, + absl::decay_t<T>>::value, + variant_internal::IndexOfConstructedType<variant, T>>::type::value, + class Tj = absl::variant_alternative_t<I, variant>, + absl::enable_if_t<std::is_constructible<Tj, T>::value>* = + nullptr> + constexpr variant(T&& t) noexcept(std::is_nothrow_constructible<Tj, T>::value) + : Base(variant_internal::EmplaceTag<I>(), absl::forward<T>(t)) {} + + // Constructs a variant of an alternative type from the arguments through + // direct-initialization. + // + // Note: If the selected constructor is a constexpr constructor, this + // constructor shall be a constexpr constructor. + template <class T, class... Args, + typename std::enable_if<std::is_constructible< + variant_internal::UnambiguousTypeOfT<variant, T>, + Args...>::value>::type* = nullptr> + constexpr explicit variant(in_place_type_t<T>, Args&&... args) + : Base(variant_internal::EmplaceTag< + variant_internal::UnambiguousIndexOf<variant, T>::value>(), + absl::forward<Args>(args)...) {} + + // Constructs a variant of an alternative type from an initializer list + // and other arguments through direct-initialization. + // + // Note: If the selected constructor is a constexpr constructor, this + // constructor shall be a constexpr constructor. + template <class T, class U, class... Args, + typename std::enable_if<std::is_constructible< + variant_internal::UnambiguousTypeOfT<variant, T>, + std::initializer_list<U>&, Args...>::value>::type* = nullptr> + constexpr explicit variant(in_place_type_t<T>, std::initializer_list<U> il, + Args&&... args) + : Base(variant_internal::EmplaceTag< + variant_internal::UnambiguousIndexOf<variant, T>::value>(), + il, absl::forward<Args>(args)...) {} + + // Constructs a variant of an alternative type from a provided index, + // through value-initialization using the provided forwarded arguments. + template <std::size_t I, class... Args, + typename std::enable_if<std::is_constructible< + variant_internal::VariantAlternativeSfinaeT<I, variant>, + Args...>::value>::type* = nullptr> + constexpr explicit variant(in_place_index_t<I>, Args&&... args) + : Base(variant_internal::EmplaceTag<I>(), absl::forward<Args>(args)...) {} + + // Constructs a variant of an alternative type from a provided index, + // through value-initialization of an initializer list and the provided + // forwarded arguments. + template <std::size_t I, class U, class... Args, + typename std::enable_if<std::is_constructible< + variant_internal::VariantAlternativeSfinaeT<I, variant>, + std::initializer_list<U>&, Args...>::value>::type* = nullptr> + constexpr explicit variant(in_place_index_t<I>, std::initializer_list<U> il, + Args&&... args) + : Base(variant_internal::EmplaceTag<I>(), il, + absl::forward<Args>(args)...) {} + + // Destructors + + // Destroys the variant's currently contained value, provided that + // `absl::valueless_by_exception()` is false. + ~variant() = default; + + // Assignment Operators + + // Copy assignement operator + variant& operator=(const variant& other) = default; + + // Move assignment operator + variant& operator=(variant&& other) /*noexcept(see above)*/ = default; + + // Converting assignment operator + // + // NOTE: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0608r1.html + // has been voted passed the design phase in the C++ standard meeting in Mar + // 2018. It will be implemented and integrated into `absl::variant`. + template < + class T, + std::size_t I = std::enable_if< + !std::is_same<absl::decay_t<T>, variant>::value, + variant_internal::IndexOfConstructedType<variant, T>>::type::value, + class Tj = absl::variant_alternative_t<I, variant>, + typename std::enable_if<std::is_assignable<Tj&, T>::value && + std::is_constructible<Tj, T>::value>::type* = + nullptr> + variant& operator=(T&& t) noexcept( + std::is_nothrow_assignable<Tj&, T>::value&& + std::is_nothrow_constructible<Tj, T>::value) { + variant_internal::visit_indices<sizeof...(Tn) + 1>( + variant_internal::VariantCoreAccess::MakeConversionAssignVisitor( + this, absl::forward<T>(t)), + index()); + + return *this; + } + + + // emplace() Functions + + // Constructs a value of the given alternative type T within the variant. + // + // Example: + // + // absl::variant<std::vector<int>, int, std::string> v; + // v.emplace<int>(99); + // v.emplace<std::string>("abc"); + template < + class T, class... Args, + typename std::enable_if<std::is_constructible< + absl::variant_alternative_t< + variant_internal::UnambiguousIndexOf<variant, T>::value, variant>, + Args...>::value>::type* = nullptr> + T& emplace(Args&&... args) { + return variant_internal::VariantCoreAccess::Replace< + variant_internal::UnambiguousIndexOf<variant, T>::value>( + this, absl::forward<Args>(args)...); + } + + // Constructs a value of the given alternative type T within the variant using + // an initializer list. + // + // Example: + // + // absl::variant<std::vector<int>, int, std::string> v; + // v.emplace<std::vector<int>>({0, 1, 2}); + template < + class T, class U, class... Args, + typename std::enable_if<std::is_constructible< + absl::variant_alternative_t< + variant_internal::UnambiguousIndexOf<variant, T>::value, variant>, + std::initializer_list<U>&, Args...>::value>::type* = nullptr> + T& emplace(std::initializer_list<U> il, Args&&... args) { + return variant_internal::VariantCoreAccess::Replace< + variant_internal::UnambiguousIndexOf<variant, T>::value>( + this, il, absl::forward<Args>(args)...); + } + + // Destroys the current value of the variant (provided that + // `absl::valueless_by_exception()` is false, and constructs a new value at + // the given index. + // + // Example: + // + // absl::variant<std::vector<int>, int, int> v; + // v.emplace<1>(99); + // v.emplace<2>(98); + // v.emplace<int>(99); // Won't compile. 'int' isn't a unique type. + template <std::size_t I, class... Args, + typename std::enable_if< + std::is_constructible<absl::variant_alternative_t<I, variant>, + Args...>::value>::type* = nullptr> + absl::variant_alternative_t<I, variant>& emplace(Args&&... args) { + return variant_internal::VariantCoreAccess::Replace<I>( + this, absl::forward<Args>(args)...); + } + + // Destroys the current value of the variant (provided that + // `absl::valueless_by_exception()` is false, and constructs a new value at + // the given index using an initializer list and the provided arguments. + // + // Example: + // + // absl::variant<std::vector<int>, int, int> v; + // v.emplace<0>({0, 1, 2}); + template <std::size_t I, class U, class... Args, + typename std::enable_if<std::is_constructible< + absl::variant_alternative_t<I, variant>, + std::initializer_list<U>&, Args...>::value>::type* = nullptr> + absl::variant_alternative_t<I, variant>& emplace(std::initializer_list<U> il, + Args&&... args) { + return variant_internal::VariantCoreAccess::Replace<I>( + this, il, absl::forward<Args>(args)...); + } + + // variant::valueless_by_exception() + // + // Returns false if and only if the variant currently holds a valid value. + constexpr bool valueless_by_exception() const noexcept { + return this->index_ == absl::variant_npos; + } + + // variant::index() + // + // Returns the index value of the variant's currently selected alternative + // type. + constexpr std::size_t index() const noexcept { return this->index_; } + + // variant::swap() + // + // Swaps the values of two variant objects. + // + // TODO(calabrese) + // `variant::swap()` and `swap()` rely on `std::is_(nothrow)_swappable()` + // which is introduced in C++17. So we assume `is_swappable()` is always + // true and `is_nothrow_swappable()` is same as `std::is_trivial()`. + void swap(variant& rhs) noexcept( + absl::conjunction<std::is_trivial<T0>, std::is_trivial<Tn>...>::value) { + return variant_internal::visit_indices<sizeof...(Tn) + 1>( + variant_internal::Swap<T0, Tn...>{this, &rhs}, rhs.index()); + } +}; + +// We need a valid declaration of variant<> for SFINAE and overload resolution +// to work properly above, but we don't need a full declaration since this type +// will never be constructed. This declaration, though incomplete, suffices. +template <> +class variant<>; + +//------------------------------------------------------------------------------ +// Relational Operators +//------------------------------------------------------------------------------ +// +// If neither operand is in the `variant::valueless_by_exception` state: +// +// * If the index of both variants is the same, the relational operator +// returns the result of the corresponding relational operator for the +// corresponding alternative type. +// * If the index of both variants is not the same, the relational operator +// returns the result of that operation applied to the value of the left +// operand's index and the value of the right operand's index. +// * If at least one operand is in the valueless_by_exception state: +// - A variant in the valueless_by_exception state is only considered equal +// to another variant in the valueless_by_exception state. +// - If exactly one operand is in the valueless_by_exception state, the +// variant in the valueless_by_exception state is less than the variant +// that is not in the valueless_by_exception state. +// +// Note: The value 1 is added to each index in the relational comparisons such +// that the index corresponding to the valueless_by_exception state wraps around +// to 0 (the lowest value for the index type), and the remaining indices stay in +// the same relative order. + +// Equal-to operator +template <typename... Types> +constexpr variant_internal::RequireAllHaveEqualT<Types...> operator==( + const variant<Types...>& a, const variant<Types...>& b) { + return (a.index() == b.index()) && + variant_internal::visit_indices<sizeof...(Types)>( + variant_internal::EqualsOp<Types...>{&a, &b}, a.index()); +} + +// Not equal operator +template <typename... Types> +constexpr variant_internal::RequireAllHaveNotEqualT<Types...> operator!=( + const variant<Types...>& a, const variant<Types...>& b) { + return (a.index() != b.index()) || + variant_internal::visit_indices<sizeof...(Types)>( + variant_internal::NotEqualsOp<Types...>{&a, &b}, a.index()); +} + +// Less-than operator +template <typename... Types> +constexpr variant_internal::RequireAllHaveLessThanT<Types...> operator<( + const variant<Types...>& a, const variant<Types...>& b) { + return (a.index() != b.index()) + ? (a.index() + 1) < (b.index() + 1) + : variant_internal::visit_indices<sizeof...(Types)>( + variant_internal::LessThanOp<Types...>{&a, &b}, a.index()); +} + +// Greater-than operator +template <typename... Types> +constexpr variant_internal::RequireAllHaveGreaterThanT<Types...> operator>( + const variant<Types...>& a, const variant<Types...>& b) { + return (a.index() != b.index()) + ? (a.index() + 1) > (b.index() + 1) + : variant_internal::visit_indices<sizeof...(Types)>( + variant_internal::GreaterThanOp<Types...>{&a, &b}, + a.index()); +} + +// Less-than or equal-to operator +template <typename... Types> +constexpr variant_internal::RequireAllHaveLessThanOrEqualT<Types...> operator<=( + const variant<Types...>& a, const variant<Types...>& b) { + return (a.index() != b.index()) + ? (a.index() + 1) < (b.index() + 1) + : variant_internal::visit_indices<sizeof...(Types)>( + variant_internal::LessThanOrEqualsOp<Types...>{&a, &b}, + a.index()); +} + +// Greater-than or equal-to operator +template <typename... Types> +constexpr variant_internal::RequireAllHaveGreaterThanOrEqualT<Types...> +operator>=(const variant<Types...>& a, const variant<Types...>& b) { + return (a.index() != b.index()) + ? (a.index() + 1) > (b.index() + 1) + : variant_internal::visit_indices<sizeof...(Types)>( + variant_internal::GreaterThanOrEqualsOp<Types...>{&a, &b}, + a.index()); +} + +} // namespace absl + +namespace std { + +// hash() +template <> // NOLINT +struct hash<absl::monostate> { + std::size_t operator()(absl::monostate) const { return 0; } +}; + +template <class... T> // NOLINT +struct hash<absl::variant<T...>> + : absl::variant_internal::VariantHashBase<absl::variant<T...>, void, + absl::remove_const_t<T>...> {}; + +} // namespace std + +#endif // ABSL_HAVE_STD_VARIANT + +namespace absl { +namespace variant_internal { + +// Helper visitor for converting a variant<Ts...>` into another type (mostly +// variant) that can be constructed from any type. +template <typename To> +struct ConversionVisitor { + template <typename T> + To operator()(T&& v) const { + return To(std::forward<T>(v)); + } +}; + +} // namespace variant_internal + +// ConvertVariantTo() +// +// Helper functions to convert an `absl::variant` to a variant of another set of +// types, provided that the alternative type of the new variant type can be +// converted from any type in the source variant. +// +// Example: +// +// absl::variant<name1, name2, float> InternalReq(const Req&); +// +// // name1 and name2 are convertible to name +// absl::variant<name, float> ExternalReq(const Req& req) { +// return absl::ConvertVariantTo<absl::variant<name, float>>( +// InternalReq(req)); +// } +template <typename To, typename Variant> +To ConvertVariantTo(Variant&& variant) { + return absl::visit(variant_internal::ConversionVisitor<To>{}, + std::forward<Variant>(variant)); +} + +} // namespace absl + +#endif // ABSL_TYPES_VARIANT_H_ |