Add 'third_party/abseil_cpp/' from commit '768eb2ca2857342673fcd462792ce04b8bac3fa3' r/781

git-subtree-dir: third_party/abseil_cpp
git-subtree-mainline: ffb2ae54beb5796cd408fbe15d2d2da09ff37adf
git-subtree-split: 768eb2ca2857342673fcd462792ce04b8bac3fa3

1 files changed, 290 insertions, 0 deletions

diff --git a/third_party/abseil_cpp/absl/container/internal/compressed_tuple.h b/third_party/abseil_cpp/absl/container/internal/compressed_tuple.h
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+++ b/third_party/abseil_cpp/absl/container/internal/compressed_tuple.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
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// Helper class to perform the Empty Base Optimization.
+// Ts can contain classes and non-classes, empty or not. For the ones that
+// are empty classes, we perform the optimization. If all types in Ts are empty
+// classes, then CompressedTuple<Ts...> is itself an empty class.
+//
+// To access the members, use member get<N>() function.
+//
+// Eg:
+//   absl::container_internal::CompressedTuple<int, T1, T2, T3> value(7, t1, t2,
+//                                                                    t3);
+//   assert(value.get<0>() == 7);
+//   T1& t1 = value.get<1>();
+//   const T2& t2 = value.get<2>();
+//   ...
+//
+// https://en.cppreference.com/w/cpp/language/ebo
+
+#ifndef ABSL_CONTAINER_INTERNAL_COMPRESSED_TUPLE_H_
+#define ABSL_CONTAINER_INTERNAL_COMPRESSED_TUPLE_H_
+
+#include <initializer_list>
+#include <tuple>
+#include <type_traits>
+#include <utility>
+
+#include "absl/utility/utility.h"
+
+#if defined(_MSC_VER) && !defined(__NVCC__)
+// We need to mark these classes with this declspec to ensure that
+// CompressedTuple happens.
+#define ABSL_INTERNAL_COMPRESSED_TUPLE_DECLSPEC __declspec(empty_bases)
+#else
+#define ABSL_INTERNAL_COMPRESSED_TUPLE_DECLSPEC
+#endif
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace container_internal {
+
+template <typename... Ts>
+class CompressedTuple;
+
+namespace internal_compressed_tuple {
+
+template <typename D, size_t I>
+struct Elem;
+template <typename... B, size_t I>
+struct Elem<CompressedTuple<B...>, I>
+    : std::tuple_element<I, std::tuple<B...>> {};
+template <typename D, size_t I>
+using ElemT = typename Elem<D, I>::type;
+
+// Use the __is_final intrinsic if available. Where it's not available, classes
+// declared with the 'final' specifier cannot be used as CompressedTuple
+// elements.
+// TODO(sbenza): Replace this with std::is_final in C++14.
+template <typename T>
+constexpr bool IsFinal() {
+#if defined(__clang__) || defined(__GNUC__)
+  return __is_final(T);
+#else
+  return false;
+#endif
+}
+
+// We can't use EBCO on other CompressedTuples because that would mean that we
+// derive from multiple Storage<> instantiations with the same I parameter,
+// and potentially from multiple identical Storage<> instantiations.  So anytime
+// we use type inheritance rather than encapsulation, we mark
+// CompressedTupleImpl, to make this easy to detect.
+struct uses_inheritance {};
+
+template <typename T>
+constexpr bool ShouldUseBase() {
+  return std::is_class<T>::value && std::is_empty<T>::value && !IsFinal<T>() &&
+         !std::is_base_of<uses_inheritance, T>::value;
+}
+
+// The storage class provides two specializations:
+//  - For empty classes, it stores T as a base class.
+//  - For everything else, it stores T as a member.
+template <typename T, size_t I,
+#if defined(_MSC_VER)
+          bool UseBase =
+              ShouldUseBase<typename std::enable_if<true, T>::type>()>
+#else
+          bool UseBase = ShouldUseBase<T>()>
+#endif
+struct Storage {
+  T value;
+  constexpr Storage() = default;
+  template <typename V>
+  explicit constexpr Storage(absl::in_place_t, V&& v)
+      : value(absl::forward<V>(v)) {}
+  constexpr const T& get() const& { return value; }
+  T& get() & { return value; }
+  constexpr const T&& get() const&& { return absl::move(*this).value; }
+  T&& get() && { return std::move(*this).value; }
+};
+
+template <typename T, size_t I>
+struct ABSL_INTERNAL_COMPRESSED_TUPLE_DECLSPEC Storage<T, I, true> : T {
+  constexpr Storage() = default;
+
+  template <typename V>
+  explicit constexpr Storage(absl::in_place_t, V&& v)
+      : T(absl::forward<V>(v)) {}
+
+  constexpr const T& get() const& { return *this; }
+  T& get() & { return *this; }
+  constexpr const T&& get() const&& { return absl::move(*this); }
+  T&& get() && { return std::move(*this); }
+};
+
+template <typename D, typename I, bool ShouldAnyUseBase>
+struct ABSL_INTERNAL_COMPRESSED_TUPLE_DECLSPEC CompressedTupleImpl;
+
+template <typename... Ts, size_t... I, bool ShouldAnyUseBase>
+struct ABSL_INTERNAL_COMPRESSED_TUPLE_DECLSPEC CompressedTupleImpl<
+    CompressedTuple<Ts...>, absl::index_sequence<I...>, ShouldAnyUseBase>
+    // We use the dummy identity function through std::integral_constant to
+    // convince MSVC of accepting and expanding I in that context. Without it
+    // you would get:
+    //   error C3548: 'I': parameter pack cannot be used in this context
+    : uses_inheritance,
+      Storage<Ts, std::integral_constant<size_t, I>::value>... {
+  constexpr CompressedTupleImpl() = default;
+  template <typename... Vs>
+  explicit constexpr CompressedTupleImpl(absl::in_place_t, Vs&&... args)
+      : Storage<Ts, I>(absl::in_place, absl::forward<Vs>(args))... {}
+  friend CompressedTuple<Ts...>;
+};
+
+template <typename... Ts, size_t... I>
+struct ABSL_INTERNAL_COMPRESSED_TUPLE_DECLSPEC CompressedTupleImpl<
+    CompressedTuple<Ts...>, absl::index_sequence<I...>, false>
+    // We use the dummy identity function as above...
+    : Storage<Ts, std::integral_constant<size_t, I>::value, false>... {
+  constexpr CompressedTupleImpl() = default;
+  template <typename... Vs>
+  explicit constexpr CompressedTupleImpl(absl::in_place_t, Vs&&... args)
+      : Storage<Ts, I, false>(absl::in_place, absl::forward<Vs>(args))... {}
+  friend CompressedTuple<Ts...>;
+};
+
+std::false_type Or(std::initializer_list<std::false_type>);
+std::true_type Or(std::initializer_list<bool>);
+
+// MSVC requires this to be done separately rather than within the declaration
+// of CompressedTuple below.
+template <typename... Ts>
+constexpr bool ShouldAnyUseBase() {
+  return decltype(
+      Or({std::integral_constant<bool, ShouldUseBase<Ts>()>()...})){};
+}
+
+template <typename T, typename V>
+using TupleElementMoveConstructible =
+    typename std::conditional<std::is_reference<T>::value,
+                              std::is_convertible<V, T>,
+                              std::is_constructible<T, V&&>>::type;
+
+template <bool SizeMatches, class T, class... Vs>
+struct TupleMoveConstructible : std::false_type {};
+
+template <class... Ts, class... Vs>
+struct TupleMoveConstructible<true, CompressedTuple<Ts...>, Vs...>
+    : std::integral_constant<
+          bool, absl::conjunction<
+                    TupleElementMoveConstructible<Ts, Vs&&>...>::value> {};
+
+template <typename T>
+struct compressed_tuple_size;
+
+template <typename... Es>
+struct compressed_tuple_size<CompressedTuple<Es...>>
+    : public std::integral_constant<std::size_t, sizeof...(Es)> {};
+
+template <class T, class... Vs>
+struct TupleItemsMoveConstructible
+    : std::integral_constant<
+          bool, TupleMoveConstructible<compressed_tuple_size<T>::value ==
+                                           sizeof...(Vs),
+                                       T, Vs...>::value> {};
+
+}  // namespace internal_compressed_tuple
+
+// Helper class to perform the Empty Base Class Optimization.
+// Ts can contain classes and non-classes, empty or not. For the ones that
+// are empty classes, we perform the CompressedTuple. If all types in Ts are
+// empty classes, then CompressedTuple<Ts...> is itself an empty class.  (This
+// does not apply when one or more of those empty classes is itself an empty
+// CompressedTuple.)
+//
+// To access the members, use member .get<N>() function.
+//
+// Eg:
+//   absl::container_internal::CompressedTuple<int, T1, T2, T3> value(7, t1, t2,
+//                                                                    t3);
+//   assert(value.get<0>() == 7);
+//   T1& t1 = value.get<1>();
+//   const T2& t2 = value.get<2>();
+//   ...
+//
+// https://en.cppreference.com/w/cpp/language/ebo
+template <typename... Ts>
+class ABSL_INTERNAL_COMPRESSED_TUPLE_DECLSPEC CompressedTuple
+    : private internal_compressed_tuple::CompressedTupleImpl<
+          CompressedTuple<Ts...>, absl::index_sequence_for<Ts...>,
+          internal_compressed_tuple::ShouldAnyUseBase<Ts...>()> {
+ private:
+  template <int I>
+  using ElemT = internal_compressed_tuple::ElemT<CompressedTuple, I>;
+
+  template <int I>
+  using StorageT = internal_compressed_tuple::Storage<ElemT<I>, I>;
+
+ public:
+  // There seems to be a bug in MSVC dealing in which using '=default' here will
+  // cause the compiler to ignore the body of other constructors. The work-
+  // around is to explicitly implement the default constructor.
+#if defined(_MSC_VER)
+  constexpr CompressedTuple() : CompressedTuple::CompressedTupleImpl() {}
+#else
+  constexpr CompressedTuple() = default;
+#endif
+  explicit constexpr CompressedTuple(const Ts&... base)
+      : CompressedTuple::CompressedTupleImpl(absl::in_place, base...) {}
+
+  template <typename First, typename... Vs,
+            absl::enable_if_t<
+                absl::conjunction<
+                    // Ensure we are not hiding default copy/move constructors.
+                    absl::negation<std::is_same<void(CompressedTuple),
+                                                void(absl::decay_t<First>)>>,
+                    internal_compressed_tuple::TupleItemsMoveConstructible<
+                        CompressedTuple<Ts...>, First, Vs...>>::value,
+                bool> = true>
+  explicit constexpr CompressedTuple(First&& first, Vs&&... base)
+      : CompressedTuple::CompressedTupleImpl(absl::in_place,
+                                             absl::forward<First>(first),
+                                             absl::forward<Vs>(base)...) {}
+
+  template <int I>
+  ElemT<I>& get() & {
+    return internal_compressed_tuple::Storage<ElemT<I>, I>::get();
+  }
+
+  template <int I>
+  constexpr const ElemT<I>& get() const& {
+    return StorageT<I>::get();
+  }
+
+  template <int I>
+  ElemT<I>&& get() && {
+    return std::move(*this).StorageT<I>::get();
+  }
+
+  template <int I>
+  constexpr const ElemT<I>&& get() const&& {
+    return absl::move(*this).StorageT<I>::get();
+  }
+};
+
+// Explicit specialization for a zero-element tuple
+// (needed to avoid ambiguous overloads for the default constructor).
+template <>
+class ABSL_INTERNAL_COMPRESSED_TUPLE_DECLSPEC CompressedTuple<> {};
+
+}  // namespace container_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#undef ABSL_INTERNAL_COMPRESSED_TUPLE_DECLSPEC
+
+#endif  // ABSL_CONTAINER_INTERNAL_COMPRESSED_TUPLE_H_