tvl-depot/absl/types/variant.h

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// 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:
//
Export of internal Abseil changes. -- 898e99cae89ca4cc27f86f719148f020d521dd58 by Abseil Team <absl-team@google.com>: Update comment. PiperOrigin-RevId: 204323401 -- b9d14db8b8a9dfb0e1cfb5967aaa0de1c4e94c42 by Abseil Team <absl-team@google.com>: Internal change PiperOrigin-RevId: 204178059 -- f3b5a667611a588aa06fea9168e997ef5cffa7ac by Abseil Team <absl-team@google.com>: Fix a potential reinterpret_cast compile error in absl::InlinedVector The current code will trigger a reinterpret_cast error enhanced by llvm r336738. PiperOrigin-RevId: 204131536 -- cc87d7a8302ad4471c1a25781d6ec19c2ce1524e by Abseil Team <absl-team@google.com>: Internal change. PiperOrigin-RevId: 203979040 -- bc5cae3cfc72af1d3e786d5a3b59a47e205afec9 by Gennadiy Rozental <rogeeff@google.com>: Internal: add internal logging hooks PiperOrigin-RevId: 203850605 -- 503655c248f557f677c920078613522b010e73c8 by Derek Mauro <dmauro@google.com>: Cleanup stacktrace_config.h Instead of listing the platforms that aren't supported, list the ones we do support, and fallback to stacktrace_unimplemented-inl.inc at the end. Previously any platform that wasn't listed gets "#error Not supported yet". GitHub issue #135 PiperOrigin-RevId: 203823079 -- cb69925c4cacc14558cf103a09f218c37f466a16 by Abseil Team <absl-team@google.com>: Fix a minor typo in absl::variant documentation. PiperOrigin-RevId: 203679877 -- 23a0e4db10039011fa5fd879fb73d2f2bbd17301 by Abseil Team <absl-team@google.com>: Format .bzl files with buildifier PiperOrigin-RevId: 203461813 -- 1ad02616bdb715dfdc7f1a73313e383f4ededa03 by Abseil Team <absl-team@google.com>: Make the absl::SleepFor() tests treat any successful retry within a 48x deadline as a total success, thereby reducing flakiness. PiperOrigin-RevId: 203401603 -- b3dccbbc6563ea0173527076a3fff21433d48f47 by Abseil Team <absl-team@google.com>: Replace config_setting.values{"compiler"} with config_setting.flag_values{"@bazel_tools//tools/cpp:compiler"} Due to changes in Bazel we need to change the way "compiler" is specified in config_setting. This will not change the behavior of the config_setting itself. PiperOrigin-RevId: 203345693 -- 170f1692537460a4ba1756d34852275899c2339b by Matt Armstrong <marmstrong@google.com>: Address test flakiness in the TimeoutTest. The basic idea is to loop forever until the expected scheduling delays are observed (within reasonable bounds), and only then assert the other invariants. PiperOrigin-RevId: 203188162 GitOrigin-RevId: 898e99cae89ca4cc27f86f719148f020d521dd58 Change-Id: Ie853ec050afa3a04c519393afe666bc03e11dc87
2018-07-12 19:34:29 +02:00
// absl::variant<int, std::string> foo = 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::CheckedAccess<
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::CheckedAccess<
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::CheckedAccess<
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::CheckedAccess<
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::CheckedAccess<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::CheckedAccess<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::CheckedAccess<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::CheckedAccess<I>(absl::move(v));
}
// get_if()
//
// Returns a pointer to the value currently stored within a given variant, if
- 07191b0f52301e1e4a790e236f7b7c2fd90561ae Disambiguates computed return type of absl::optional logi... by Abseil Team <absl-team@google.com> - acd95f8ec4e6ec1587cb198c7f40af3c81094d92 Release container benchmarks. by Alex Strelnikov <strel@google.com> - 80f596b6b7c5e06453e778c16527d5a0e85f8413 Allow absl::base_internal::AtomicHook to have a default v... by Derek Mauro <dmauro@google.com> - 8402631546af8bcbd4acdf897d0cdfb805ad544a Release thread_identity benchmark. by Alex Strelnikov <strel@google.com> - 6dcb1e90fefb8556ce4654983d3a73c7585b4b99 Fix spelling error in variant.h by Abseil Team <absl-team@google.com> - faa8a81e1442018c0d400b09a595a5be55074715 Run tests from CMake. The CI is currently Linux only, fo... by Jon Cohen <cohenjon@google.com> - 745ed6db574f931f2ec3a88e964fb03a5f22f816 Internal change. by Derek Mauro <dmauro@google.com> - 23facd7d1c5f43ac8181b016ee4acc5955f048c1 absl::variant exception safety test. by Xiaoyi Zhang <zhangxy@google.com> - c18e21e7cf8f6e83ae9d90e536e886409dd6cf68 Reinstate the syntax check on time-zone abbreviations now... by Abseil Team <absl-team@google.com> - da469f4314f0c820665a2b5b9477af9462b23e42 Import CCTZ changes to internal copy. by Shaindel Schwartz <shaindel@google.com> - 44ea35843517be03ab256b69449ccfea64352621 Import CCTZ changes to internal copy. by Abseil Team <absl-team@google.com> - 55d1105312687c6093950fac831c7540f49045b5 Import CCTZ changes to internal copy. by Greg Falcon <gfalcon@google.com> - 58d7965ad274406410b6d833213eca04d41c6867 Add zoneinfo as a data dependency to the //absl/time tests. by Shaindel Schwartz <shaindel@google.com> - 6acc50146f9ff29015bfaaa5bf9900691f839da5 Change benchmark target type from cc_test to cc_binary. by Alex Strelnikov <strel@google.com> - db3fbdae8f9f285a466f7a070326b1ce43b6a0dd Update WORKSPACE for C++ microbenchmarks and release algo... by Alex Strelnikov <strel@google.com> - 0869ae168255242af651853ed01719166d8cebf6 Update to Bazel version 0.13.0. by Abseil Team <absl-team@google.com> - e507dd53ab788964207fdf27d31b72a33c296fab Add missing include of cstdio by Abseil Team <absl-team@google.com> GitOrigin-RevId: 07191b0f52301e1e4a790e236f7b7c2fd90561ae Change-Id: I90994cf2b438fbec894724dcd9b90882281eef56
2018-05-04 18:58:56 +02:00
// present, using either a unique alternative type amongst 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(
variant_internal::VariantCoreAccess::Access<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(
variant_internal::VariantCoreAccess::Access<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.
// absl::variant<int, std::string> foo = std::string("foo");
// GetVariant visitor;
// absl::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::
VisitIndices<variant_size<absl::decay_t<Variants> >::value...>::Run(
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>...>::value,
"Attempted to instantiate a variant containing a non-object "
"type.");
// Intentionally not qualifing `negation` with `absl::` to work around a bug
// in MSVC 2015 with inline namespace and variadic template.
static_assert(absl::conjunction<negation<std::is_array<T0> >,
negation<std::is_array<Tn> >...>::value,
"Attempted to instantiate a variant containing an array type.");
static_assert(absl::conjunction<std::is_nothrow_destructible<T0>,
std::is_nothrow_destructible<Tn>...>::value,
"Attempted to instantiate a variant containing a non-nothrow "
"destructible 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::VisitIndices<sizeof...(Tn) + 1>::Run(
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::VisitIndices<sizeof...(Tn) + 1>::Run(
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::VisitIndices<sizeof...(Types)>::Run(
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::VisitIndices<sizeof...(Types)>::Run(
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::VisitIndices<sizeof...(Types)>::Run(
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::VisitIndices<sizeof...(Types)>::Run(
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::VisitIndices<sizeof...(Types)>::Run(
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::VisitIndices<sizeof...(Types)>::Run(
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_