850 lines
33 KiB
C++
850 lines
33 KiB
C++
// Copyright 2018 The Abseil Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// https://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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//
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// -----------------------------------------------------------------------------
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// variant.h
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// -----------------------------------------------------------------------------
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//
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// This header file defines an `absl::variant` type for holding a type-safe
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// value of some prescribed set of types (noted as alternative types), and
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// associated functions for managing variants.
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//
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// The `absl::variant` type is a form of type-safe union. An `absl::variant`
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// should always hold a value of one of its alternative types (except in the
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// "valueless by exception state" -- see below). A default-constructed
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// `absl::variant` will hold the value of its first alternative type, provided
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// it is default-constructable.
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//
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// In exceptional cases due to error, an `absl::variant` can hold no
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// value (known as a "valueless by exception" state), though this is not the
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// norm.
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//
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// As with `absl::optional`, an `absl::variant` -- when it holds a value --
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// allocates a value of that type directly within the `variant` itself; it
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// cannot hold a reference, array, or the type `void`; it can, however, hold a
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// pointer to externally managed memory.
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//
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// `absl::variant` is a C++11 compatible version of the C++17 `std::variant`
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// abstraction and is designed to be a drop-in replacement for code compliant
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// with C++17.
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#ifndef ABSL_TYPES_VARIANT_H_
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#define ABSL_TYPES_VARIANT_H_
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#include "absl/base/config.h"
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#include "absl/utility/utility.h"
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#ifdef ABSL_HAVE_STD_VARIANT
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#include <variant>
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namespace absl {
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using std::bad_variant_access;
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using std::get;
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using std::get_if;
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using std::holds_alternative;
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using std::monostate;
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using std::variant;
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using std::variant_alternative;
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using std::variant_alternative_t;
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using std::variant_npos;
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using std::variant_size;
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using std::variant_size_v;
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using std::visit;
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} // namespace absl
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#else // ABSL_HAVE_STD_VARIANT
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#include <functional>
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#include <new>
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#include <type_traits>
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#include <utility>
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#include "absl/base/macros.h"
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#include "absl/base/port.h"
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#include "absl/meta/type_traits.h"
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#include "absl/types/internal/variant.h"
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namespace absl {
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// -----------------------------------------------------------------------------
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// absl::variant
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// -----------------------------------------------------------------------------
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//
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// An `absl::variant` type is a form of type-safe union. An `absl::variant` --
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// except in exceptional cases -- always holds a value of one of its alternative
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// types.
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//
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// Example:
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//
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// // Construct a variant that holds either an integer or a std::string and
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// // assign it to a std::string.
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// absl::variant<int, std::string> v = std::string("abc");
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//
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// // A default-contructed variant will hold a value-initialized value of
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// // the first alternative type.
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// auto a = absl::variant<int, std::string>(); // Holds an int of value '0'.
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//
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// // variants are assignable.
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//
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// // copy assignment
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// auto v1 = absl::variant<int, std::string>("abc");
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// auto v2 = absl::variant<int, std::string>(10);
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// v2 = v1; // copy assign
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//
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// // move assignment
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// auto v1 = absl::variant<int, std::string>("abc");
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// v1 = absl::variant<int, std::string>(10);
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//
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// // assignment through type conversion
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// a = 128; // variant contains int
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// a = "128"; // variant contains std::string
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//
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// An `absl::variant` holding a value of one of its alternative types `T` holds
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// an allocation of `T` directly within the variant itself. An `absl::variant`
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// is not allowed to allocate additional storage, such as dynamic memory, to
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// allocate the contained value. The contained value shall be allocated in a
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// region of the variant storage suitably aligned for all alternative types.
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template <typename... Ts>
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class variant;
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// swap()
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//
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// Swaps two `absl::variant` values. This function is equivalent to `v.swap(w)`
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// where `v` and `w` are `absl::variant` types.
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//
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// Note that this function requires all alternative types to be both swappable
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// and move-constructible, because any two variants may refer to either the same
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// type (in which case, they will be swapped) or to two different types (in
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// which case the values will need to be moved).
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//
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template <typename... Ts>
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void swap(variant<Ts...>& v, variant<Ts...>& w) noexcept(noexcept(v.swap(w))) {
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v.swap(w);
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}
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// variant_size
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//
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// Returns the number of alternative types available for a given `absl::variant`
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// type as a compile-time constant expression. As this is a class template, it
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// is not generally useful for accessing the number of alternative types of
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// any given `absl::variant` instance.
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//
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// Example:
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//
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// auto a = absl::variant<int, std::string>;
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// constexpr int num_types =
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// absl::variant_size<absl::variant<int, std::string>>();
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//
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// // You can also use the member constant `value`.
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// constexpr int num_types =
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// absl::variant_size<absl::variant<int, std::string>>::value;
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//
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// // `absl::variant_size` is more valuable for use in generic code:
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// template <typename Variant>
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// constexpr bool IsVariantMultivalue() {
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// return absl::variant_size<Variant>() > 1;
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// }
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//
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// Note that the set of cv-qualified specializations of `variant_size` are
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// provided to ensure that those specializations compile (especially when passed
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// within template logic).
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template <class T>
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struct variant_size;
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template <class... Ts>
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struct variant_size<variant<Ts...>>
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: std::integral_constant<std::size_t, sizeof...(Ts)> {};
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// Specialization of `variant_size` for const qualified variants.
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template <class T>
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struct variant_size<const T> : variant_size<T>::type {};
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// Specialization of `variant_size` for volatile qualified variants.
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template <class T>
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struct variant_size<volatile T> : variant_size<T>::type {};
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// Specialization of `variant_size` for const volatile qualified variants.
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template <class T>
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struct variant_size<const volatile T> : variant_size<T>::type {};
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// variant_alternative
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//
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// Returns the alternative type for a given `absl::variant` at the passed
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// index value as a compile-time constant expression. As this is a class
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// template resulting in a type, it is not useful for access of the run-time
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// value of any given `absl::variant` variable.
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//
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// Example:
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//
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// // The type of the 0th alternative is "int".
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// using alternative_type_0
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// = absl::variant_alternative<0, absl::variant<int, std::string>>::type;
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//
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// static_assert(std::is_same<alternative_type_0, int>::value, "");
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//
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// // `absl::variant_alternative` is more valuable for use in generic code:
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// template <typename Variant>
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// constexpr bool IsFirstElementTrivial() {
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// return std::is_trivial_v<variant_alternative<0, Variant>::type>;
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// }
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//
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// Note that the set of cv-qualified specializations of `variant_alternative`
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// are provided to ensure that those specializations compile (especially when
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// passed within template logic).
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template <std::size_t I, class T>
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struct variant_alternative;
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template <std::size_t I, class... Types>
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struct variant_alternative<I, variant<Types...>> {
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using type =
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variant_internal::VariantAlternativeSfinaeT<I, variant<Types...>>;
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};
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// Specialization of `variant_alternative` for const qualified variants.
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template <std::size_t I, class T>
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struct variant_alternative<I, const T> {
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using type = const typename variant_alternative<I, T>::type;
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};
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// Specialization of `variant_alternative` for volatile qualified variants.
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template <std::size_t I, class T>
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struct variant_alternative<I, volatile T> {
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using type = volatile typename variant_alternative<I, T>::type;
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};
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// Specialization of `variant_alternative` for const volatile qualified
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// variants.
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template <std::size_t I, class T>
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struct variant_alternative<I, const volatile T> {
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using type = const volatile typename variant_alternative<I, T>::type;
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};
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// Template type alias for variant_alternative<I, T>::type.
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//
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// Example:
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//
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// using alternative_type_0
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// = absl::variant_alternative_t<0, absl::variant<int, std::string>>;
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// static_assert(std::is_same<alternative_type_0, int>::value, "");
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template <std::size_t I, class T>
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using variant_alternative_t = typename variant_alternative<I, T>::type;
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// holds_alternative()
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//
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// Checks whether the given variant currently holds a given alternative type,
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// returning `true` if so.
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//
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// Example:
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//
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// absl::variant<int, std::string> foo = 42;
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// if (absl::holds_alternative<int>(foo)) {
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// std::cout << "The variant holds an integer";
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// }
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template <class T, class... Types>
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constexpr bool holds_alternative(const variant<Types...>& v) noexcept {
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static_assert(
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variant_internal::UnambiguousIndexOfImpl<variant<Types...>, T,
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0>::value != sizeof...(Types),
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"The type T must occur exactly once in Types...");
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return v.index() ==
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variant_internal::UnambiguousIndexOf<variant<Types...>, T>::value;
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}
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// get()
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//
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// Returns a reference to the value currently within a given variant, using
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// either a unique alternative type amongst the variant's set of alternative
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// types, or the variant's index value. Attempting to get a variant's value
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// using a type that is not unique within the variant's set of alternative types
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// is a compile-time error. If the index of the alternative being specified is
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// different from the index of the alternative that is currently stored, throws
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// `absl::bad_variant_access`.
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//
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// Example:
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//
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// auto a = absl::variant<int, std::string>;
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//
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// // Get the value by type (if unique).
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// int i = absl::get<int>(a);
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//
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// auto b = absl::variant<int, int>;
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//
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// // Getting the value by a type that is not unique is ill-formed.
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// int j = absl::get<int>(b); // Compile Error!
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//
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// // Getting value by index not ambiguous and allowed.
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// int k = absl::get<1>(b);
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// Overload for getting a variant's lvalue by type.
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template <class T, class... Types>
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constexpr T& get(variant<Types...>& v) { // NOLINT
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return variant_internal::VariantCoreAccess::CheckedAccess<
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variant_internal::IndexOf<T, Types...>::value>(v);
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}
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// Overload for getting a variant's rvalue by type.
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// Note: `absl::move()` is required to allow use of constexpr in C++11.
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template <class T, class... Types>
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constexpr T&& get(variant<Types...>&& v) {
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return variant_internal::VariantCoreAccess::CheckedAccess<
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variant_internal::IndexOf<T, Types...>::value>(absl::move(v));
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}
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// Overload for getting a variant's const lvalue by type.
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template <class T, class... Types>
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constexpr const T& get(const variant<Types...>& v) {
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return variant_internal::VariantCoreAccess::CheckedAccess<
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variant_internal::IndexOf<T, Types...>::value>(v);
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}
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// Overload for getting a variant's const rvalue by type.
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// Note: `absl::move()` is required to allow use of constexpr in C++11.
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template <class T, class... Types>
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constexpr const T&& get(const variant<Types...>&& v) {
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return variant_internal::VariantCoreAccess::CheckedAccess<
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variant_internal::IndexOf<T, Types...>::value>(absl::move(v));
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}
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// Overload for getting a variant's lvalue by index.
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template <std::size_t I, class... Types>
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constexpr variant_alternative_t<I, variant<Types...>>& get(
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variant<Types...>& v) { // NOLINT
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return variant_internal::VariantCoreAccess::CheckedAccess<I>(v);
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}
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// Overload for getting a variant's rvalue by index.
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// Note: `absl::move()` is required to allow use of constexpr in C++11.
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template <std::size_t I, class... Types>
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constexpr variant_alternative_t<I, variant<Types...>>&& get(
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variant<Types...>&& v) {
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return variant_internal::VariantCoreAccess::CheckedAccess<I>(absl::move(v));
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}
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// Overload for getting a variant's const lvalue by index.
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template <std::size_t I, class... Types>
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constexpr const variant_alternative_t<I, variant<Types...>>& get(
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const variant<Types...>& v) {
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return variant_internal::VariantCoreAccess::CheckedAccess<I>(v);
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}
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// Overload for getting a variant's const rvalue by index.
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// Note: `absl::move()` is required to allow use of constexpr in C++11.
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template <std::size_t I, class... Types>
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constexpr const variant_alternative_t<I, variant<Types...>>&& get(
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const variant<Types...>&& v) {
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return variant_internal::VariantCoreAccess::CheckedAccess<I>(absl::move(v));
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}
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// get_if()
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//
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// Returns a pointer to the value currently stored within a given variant, if
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// present, using either a unique alternative type amongst the variant's set of
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// alternative types, or the variant's index value. If such a value does not
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// exist, returns `nullptr`.
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//
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// As with `get`, attempting to get a variant's value using a type that is not
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// unique within the variant's set of alternative types is a compile-time error.
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// Overload for getting a pointer to the value stored in the given variant by
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// index.
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template <std::size_t I, class... Types>
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constexpr absl::add_pointer_t<variant_alternative_t<I, variant<Types...>>>
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get_if(variant<Types...>* v) noexcept {
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return (v != nullptr && v->index() == I)
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? std::addressof(
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variant_internal::VariantCoreAccess::Access<I>(*v))
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: nullptr;
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}
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// Overload for getting a pointer to the const value stored in the given
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// variant by index.
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template <std::size_t I, class... Types>
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constexpr absl::add_pointer_t<const variant_alternative_t<I, variant<Types...>>>
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get_if(const variant<Types...>* v) noexcept {
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return (v != nullptr && v->index() == I)
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? std::addressof(
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variant_internal::VariantCoreAccess::Access<I>(*v))
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: nullptr;
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}
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// Overload for getting a pointer to the value stored in the given variant by
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// type.
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template <class T, class... Types>
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constexpr absl::add_pointer_t<T> get_if(variant<Types...>* v) noexcept {
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return absl::get_if<variant_internal::IndexOf<T, Types...>::value>(v);
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}
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// Overload for getting a pointer to the const value stored in the given variant
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// by type.
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template <class T, class... Types>
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constexpr absl::add_pointer_t<const T> get_if(
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const variant<Types...>* v) noexcept {
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return absl::get_if<variant_internal::IndexOf<T, Types...>::value>(v);
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}
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// visit()
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//
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// Calls a provided functor on a given set of variants. `absl::visit()` is
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// commonly used to conditionally inspect the state of a given variant (or set
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// of variants).
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//
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// The functor must return the same type when called with any of the variants'
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// alternatives.
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//
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// Example:
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//
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// // Define a visitor functor
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// struct GetVariant {
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// template<typename T>
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// void operator()(const T& i) const {
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// std::cout << "The variant's value is: " << i;
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// }
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// };
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//
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// // Declare our variant, and call `absl::visit()` on it.
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// // Note that `GetVariant()` returns void in either case.
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// absl::variant<int, std::string> foo = std::string("foo");
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// GetVariant visitor;
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// absl::visit(visitor, foo); // Prints `The variant's value is: foo'
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template <typename Visitor, typename... Variants>
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variant_internal::VisitResult<Visitor, Variants...> visit(Visitor&& vis,
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Variants&&... vars) {
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return variant_internal::
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VisitIndices<variant_size<absl::decay_t<Variants> >::value...>::Run(
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variant_internal::PerformVisitation<Visitor, Variants...>{
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std::forward_as_tuple(absl::forward<Variants>(vars)...),
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absl::forward<Visitor>(vis)},
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vars.index()...);
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}
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// monostate
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//
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// The monostate class serves as a first alternative type for a variant for
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// which the first variant type is otherwise not default-constructible.
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struct monostate {};
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// `absl::monostate` Relational Operators
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constexpr bool operator<(monostate, monostate) noexcept { return false; }
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constexpr bool operator>(monostate, monostate) noexcept { return false; }
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constexpr bool operator<=(monostate, monostate) noexcept { return true; }
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constexpr bool operator>=(monostate, monostate) noexcept { return true; }
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constexpr bool operator==(monostate, monostate) noexcept { return true; }
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constexpr bool operator!=(monostate, monostate) noexcept { return false; }
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//------------------------------------------------------------------------------
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// `absl::variant` Template Definition
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//------------------------------------------------------------------------------
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template <typename T0, typename... Tn>
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class variant<T0, Tn...> : private variant_internal::VariantBase<T0, Tn...> {
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static_assert(absl::conjunction<std::is_object<T0>,
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std::is_object<Tn>...>::value,
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"Attempted to instantiate a variant containing a non-object "
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"type.");
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// Intentionally not qualifying `negation` with `absl::` to work around a bug
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// in MSVC 2015 with inline namespace and variadic template.
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static_assert(absl::conjunction<negation<std::is_array<T0> >,
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negation<std::is_array<Tn> >...>::value,
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"Attempted to instantiate a variant containing an array type.");
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static_assert(absl::conjunction<std::is_nothrow_destructible<T0>,
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std::is_nothrow_destructible<Tn>...>::value,
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"Attempted to instantiate a variant containing a non-nothrow "
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"destructible type.");
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friend struct variant_internal::VariantCoreAccess;
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private:
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using Base = variant_internal::VariantBase<T0, Tn...>;
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public:
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// Constructors
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// Constructs a variant holding a default-initialized value of the first
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// alternative type.
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constexpr variant() /*noexcept(see 111above)*/ = default;
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// Copy constructor, standard semantics
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variant(const variant& other) = default;
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// Move constructor, standard semantics
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variant(variant&& other) /*noexcept(see above)*/ = default;
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// Constructs a variant of an alternative type specified by overload
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// resolution of the provided forwarding arguments through
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// direct-initialization.
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//
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// Note: If the selected constructor is a constexpr constructor, this
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// constructor shall be a constexpr constructor.
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//
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// NOTE: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0608r1.html
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// has been voted passed the design phase in the C++ standard meeting in Mar
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// 2018. It will be implemented and integrated into `absl::variant`.
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template <
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class T,
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std::size_t I = std::enable_if<
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variant_internal::IsNeitherSelfNorInPlace<variant,
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absl::decay_t<T>>::value,
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variant_internal::IndexOfConstructedType<variant, T>>::type::value,
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class Tj = absl::variant_alternative_t<I, variant>,
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absl::enable_if_t<std::is_constructible<Tj, T>::value>* =
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nullptr>
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constexpr variant(T&& t) noexcept(std::is_nothrow_constructible<Tj, T>::value)
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: Base(variant_internal::EmplaceTag<I>(), absl::forward<T>(t)) {}
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// Constructs a variant of an alternative type from the arguments through
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// direct-initialization.
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//
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// Note: If the selected constructor is a constexpr constructor, this
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// constructor shall be a constexpr constructor.
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template <class T, class... Args,
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typename std::enable_if<std::is_constructible<
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variant_internal::UnambiguousTypeOfT<variant, T>,
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Args...>::value>::type* = nullptr>
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constexpr explicit variant(in_place_type_t<T>, Args&&... args)
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: Base(variant_internal::EmplaceTag<
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variant_internal::UnambiguousIndexOf<variant, T>::value>(),
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absl::forward<Args>(args)...) {}
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// Constructs a variant of an alternative type from an initializer list
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// and other arguments through direct-initialization.
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//
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// Note: If the selected constructor is a constexpr constructor, this
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// constructor shall be a constexpr constructor.
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template <class T, class U, class... Args,
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typename std::enable_if<std::is_constructible<
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variant_internal::UnambiguousTypeOfT<variant, T>,
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std::initializer_list<U>&, Args...>::value>::type* = nullptr>
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constexpr explicit variant(in_place_type_t<T>, std::initializer_list<U> il,
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Args&&... args)
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: Base(variant_internal::EmplaceTag<
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variant_internal::UnambiguousIndexOf<variant, T>::value>(),
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il, absl::forward<Args>(args)...) {}
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// Constructs a variant of an alternative type from a provided index,
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// through value-initialization using the provided forwarded arguments.
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template <std::size_t I, class... Args,
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typename std::enable_if<std::is_constructible<
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variant_internal::VariantAlternativeSfinaeT<I, variant>,
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Args...>::value>::type* = nullptr>
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constexpr explicit variant(in_place_index_t<I>, Args&&... args)
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: Base(variant_internal::EmplaceTag<I>(), absl::forward<Args>(args)...) {}
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// Constructs a variant of an alternative type from a provided index,
|
|
// through value-initialization of an initializer list and the provided
|
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// forwarded arguments.
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template <std::size_t I, class U, class... Args,
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typename std::enable_if<std::is_constructible<
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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,
|
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Args&&... args)
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: Base(variant_internal::EmplaceTag<I>(), il,
|
|
absl::forward<Args>(args)...) {}
|
|
|
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// Destructors
|
|
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// Destroys the variant's currently contained value, provided that
|
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// `absl::valueless_by_exception()` is false.
|
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~variant() = default;
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|
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// Assignment Operators
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|
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// Copy assignment operator
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variant& operator=(const variant& other) = default;
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|
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// Move assignment operator
|
|
variant& operator=(variant&& other) /*noexcept(see above)*/ = default;
|
|
|
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// 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_
|