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, 350 insertions, 0 deletions

diff --git a/third_party/abseil_cpp/absl/utility/utility.h b/third_party/abseil_cpp/absl/utility/utility.h
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+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// This header file contains C++11 versions of standard <utility> header
+// abstractions available within C++14 and C++17, and are designed to be drop-in
+// replacement for code compliant with C++14 and C++17.
+//
+// The following abstractions are defined:
+//
+//   * integer_sequence<T, Ints...>  == std::integer_sequence<T, Ints...>
+//   * index_sequence<Ints...>       == std::index_sequence<Ints...>
+//   * make_integer_sequence<T, N>   == std::make_integer_sequence<T, N>
+//   * make_index_sequence<N>        == std::make_index_sequence<N>
+//   * index_sequence_for<Ts...>     == std::index_sequence_for<Ts...>
+//   * apply<Functor, Tuple>         == std::apply<Functor, Tuple>
+//   * exchange<T>                   == std::exchange<T>
+//   * make_from_tuple<T>            == std::make_from_tuple<T>
+//
+// This header file also provides the tag types `in_place_t`, `in_place_type_t`,
+// and `in_place_index_t`, as well as the constant `in_place`, and
+// `constexpr` `std::move()` and `std::forward()` implementations in C++11.
+//
+// References:
+//
+//  https://en.cppreference.com/w/cpp/utility/integer_sequence
+//  https://en.cppreference.com/w/cpp/utility/apply
+//  http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3658.html
+
+#ifndef ABSL_UTILITY_UTILITY_H_
+#define ABSL_UTILITY_UTILITY_H_
+
+#include <cstddef>
+#include <cstdlib>
+#include <tuple>
+#include <utility>
+
+#include "absl/base/config.h"
+#include "absl/base/internal/inline_variable.h"
+#include "absl/base/internal/invoke.h"
+#include "absl/meta/type_traits.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+// integer_sequence
+//
+// Class template representing a compile-time integer sequence. An instantiation
+// of `integer_sequence<T, Ints...>` has a sequence of integers encoded in its
+// type through its template arguments (which is a common need when
+// working with C++11 variadic templates). `absl::integer_sequence` is designed
+// to be a drop-in replacement for C++14's `std::integer_sequence`.
+//
+// Example:
+//
+//   template< class T, T... Ints >
+//   void user_function(integer_sequence<T, Ints...>);
+//
+//   int main()
+//   {
+//     // user_function's `T` will be deduced to `int` and `Ints...`
+//     // will be deduced to `0, 1, 2, 3, 4`.
+//     user_function(make_integer_sequence<int, 5>());
+//   }
+template <typename T, T... Ints>
+struct integer_sequence {
+  using value_type = T;
+  static constexpr size_t size() noexcept { return sizeof...(Ints); }
+};
+
+// index_sequence
+//
+// A helper template for an `integer_sequence` of `size_t`,
+// `absl::index_sequence` is designed to be a drop-in replacement for C++14's
+// `std::index_sequence`.
+template <size_t... Ints>
+using index_sequence = integer_sequence<size_t, Ints...>;
+
+namespace utility_internal {
+
+template <typename Seq, size_t SeqSize, size_t Rem>
+struct Extend;
+
+// Note that SeqSize == sizeof...(Ints). It's passed explicitly for efficiency.
+template <typename T, T... Ints, size_t SeqSize>
+struct Extend<integer_sequence<T, Ints...>, SeqSize, 0> {
+  using type = integer_sequence<T, Ints..., (Ints + SeqSize)...>;
+};
+
+template <typename T, T... Ints, size_t SeqSize>
+struct Extend<integer_sequence<T, Ints...>, SeqSize, 1> {
+  using type = integer_sequence<T, Ints..., (Ints + SeqSize)..., 2 * SeqSize>;
+};
+
+// Recursion helper for 'make_integer_sequence<T, N>'.
+// 'Gen<T, N>::type' is an alias for 'integer_sequence<T, 0, 1, ... N-1>'.
+template <typename T, size_t N>
+struct Gen {
+  using type =
+      typename Extend<typename Gen<T, N / 2>::type, N / 2, N % 2>::type;
+};
+
+template <typename T>
+struct Gen<T, 0> {
+  using type = integer_sequence<T>;
+};
+
+template <typename T>
+struct InPlaceTypeTag {
+  explicit InPlaceTypeTag() = delete;
+  InPlaceTypeTag(const InPlaceTypeTag&) = delete;
+  InPlaceTypeTag& operator=(const InPlaceTypeTag&) = delete;
+};
+
+template <size_t I>
+struct InPlaceIndexTag {
+  explicit InPlaceIndexTag() = delete;
+  InPlaceIndexTag(const InPlaceIndexTag&) = delete;
+  InPlaceIndexTag& operator=(const InPlaceIndexTag&) = delete;
+};
+
+}  // namespace utility_internal
+
+// Compile-time sequences of integers
+
+// make_integer_sequence
+//
+// This template alias is equivalent to
+// `integer_sequence<int, 0, 1, ..., N-1>`, and is designed to be a drop-in
+// replacement for C++14's `std::make_integer_sequence`.
+template <typename T, T N>
+using make_integer_sequence = typename utility_internal::Gen<T, N>::type;
+
+// make_index_sequence
+//
+// This template alias is equivalent to `index_sequence<0, 1, ..., N-1>`,
+// and is designed to be a drop-in replacement for C++14's
+// `std::make_index_sequence`.
+template <size_t N>
+using make_index_sequence = make_integer_sequence<size_t, N>;
+
+// index_sequence_for
+//
+// Converts a typename pack into an index sequence of the same length, and
+// is designed to be a drop-in replacement for C++14's
+// `std::index_sequence_for()`
+template <typename... Ts>
+using index_sequence_for = make_index_sequence<sizeof...(Ts)>;
+
+// Tag types
+
+#ifdef ABSL_USES_STD_OPTIONAL
+
+using std::in_place_t;
+using std::in_place;
+
+#else  // ABSL_USES_STD_OPTIONAL
+
+// in_place_t
+//
+// Tag type used to specify in-place construction, such as with
+// `absl::optional`, designed to be a drop-in replacement for C++17's
+// `std::in_place_t`.
+struct in_place_t {};
+
+ABSL_INTERNAL_INLINE_CONSTEXPR(in_place_t, in_place, {});
+
+#endif  // ABSL_USES_STD_OPTIONAL
+
+#if defined(ABSL_USES_STD_ANY) || defined(ABSL_USES_STD_VARIANT)
+using std::in_place_type;
+using std::in_place_type_t;
+#else
+
+// in_place_type_t
+//
+// Tag type used for in-place construction when the type to construct needs to
+// be specified, such as with `absl::any`, designed to be a drop-in replacement
+// for C++17's `std::in_place_type_t`.
+template <typename T>
+using in_place_type_t = void (*)(utility_internal::InPlaceTypeTag<T>);
+
+template <typename T>
+void in_place_type(utility_internal::InPlaceTypeTag<T>) {}
+#endif  // ABSL_USES_STD_ANY || ABSL_USES_STD_VARIANT
+
+#ifdef ABSL_USES_STD_VARIANT
+using std::in_place_index;
+using std::in_place_index_t;
+#else
+
+// in_place_index_t
+//
+// Tag type used for in-place construction when the type to construct needs to
+// be specified, such as with `absl::any`, designed to be a drop-in replacement
+// for C++17's `std::in_place_index_t`.
+template <size_t I>
+using in_place_index_t = void (*)(utility_internal::InPlaceIndexTag<I>);
+
+template <size_t I>
+void in_place_index(utility_internal::InPlaceIndexTag<I>) {}
+#endif  // ABSL_USES_STD_VARIANT
+
+// Constexpr move and forward
+
+// move()
+//
+// A constexpr version of `std::move()`, designed to be a drop-in replacement
+// for C++14's `std::move()`.
+template <typename T>
+constexpr absl::remove_reference_t<T>&& move(T&& t) noexcept {
+  return static_cast<absl::remove_reference_t<T>&&>(t);
+}
+
+// forward()
+//
+// A constexpr version of `std::forward()`, designed to be a drop-in replacement
+// for C++14's `std::forward()`.
+template <typename T>
+constexpr T&& forward(
+    absl::remove_reference_t<T>& t) noexcept {  // NOLINT(runtime/references)
+  return static_cast<T&&>(t);
+}
+
+namespace utility_internal {
+// Helper method for expanding tuple into a called method.
+template <typename Functor, typename Tuple, std::size_t... Indexes>
+auto apply_helper(Functor&& functor, Tuple&& t, index_sequence<Indexes...>)
+    -> decltype(absl::base_internal::Invoke(
+        absl::forward<Functor>(functor),
+        std::get<Indexes>(absl::forward<Tuple>(t))...)) {
+  return absl::base_internal::Invoke(
+      absl::forward<Functor>(functor),
+      std::get<Indexes>(absl::forward<Tuple>(t))...);
+}
+
+}  // namespace utility_internal
+
+// apply
+//
+// Invokes a Callable using elements of a tuple as its arguments.
+// Each element of the tuple corresponds to an argument of the call (in order).
+// Both the Callable argument and the tuple argument are perfect-forwarded.
+// For member-function Callables, the first tuple element acts as the `this`
+// pointer. `absl::apply` is designed to be a drop-in replacement for C++17's
+// `std::apply`. Unlike C++17's `std::apply`, this is not currently `constexpr`.
+//
+// Example:
+//
+//   class Foo {
+//    public:
+//     void Bar(int);
+//   };
+//   void user_function1(int, std::string);
+//   void user_function2(std::unique_ptr<Foo>);
+//   auto user_lambda = [](int, int) {};
+//
+//   int main()
+//   {
+//       std::tuple<int, std::string> tuple1(42, "bar");
+//       // Invokes the first user function on int, std::string.
+//       absl::apply(&user_function1, tuple1);
+//
+//       std::tuple<std::unique_ptr<Foo>> tuple2(absl::make_unique<Foo>());
+//       // Invokes the user function that takes ownership of the unique
+//       // pointer.
+//       absl::apply(&user_function2, std::move(tuple2));
+//
+//       auto foo = absl::make_unique<Foo>();
+//       std::tuple<Foo*, int> tuple3(foo.get(), 42);
+//       // Invokes the method Bar on foo with one argument, 42.
+//       absl::apply(&Foo::Bar, tuple3);
+//
+//       std::tuple<int, int> tuple4(8, 9);
+//       // Invokes a lambda.
+//       absl::apply(user_lambda, tuple4);
+//   }
+template <typename Functor, typename Tuple>
+auto apply(Functor&& functor, Tuple&& t)
+    -> decltype(utility_internal::apply_helper(
+        absl::forward<Functor>(functor), absl::forward<Tuple>(t),
+        absl::make_index_sequence<std::tuple_size<
+            typename std::remove_reference<Tuple>::type>::value>{})) {
+  return utility_internal::apply_helper(
+      absl::forward<Functor>(functor), absl::forward<Tuple>(t),
+      absl::make_index_sequence<std::tuple_size<
+          typename std::remove_reference<Tuple>::type>::value>{});
+}
+
+// exchange
+//
+// Replaces the value of `obj` with `new_value` and returns the old value of
+// `obj`.  `absl::exchange` is designed to be a drop-in replacement for C++14's
+// `std::exchange`.
+//
+// Example:
+//
+//   Foo& operator=(Foo&& other) {
+//     ptr1_ = absl::exchange(other.ptr1_, nullptr);
+//     int1_ = absl::exchange(other.int1_, -1);
+//     return *this;
+//   }
+template <typename T, typename U = T>
+T exchange(T& obj, U&& new_value) {
+  T old_value = absl::move(obj);
+  obj = absl::forward<U>(new_value);
+  return old_value;
+}
+
+namespace utility_internal {
+template <typename T, typename Tuple, size_t... I>
+T make_from_tuple_impl(Tuple&& tup, absl::index_sequence<I...>) {
+  return T(std::get<I>(std::forward<Tuple>(tup))...);
+}
+}  // namespace utility_internal
+
+// make_from_tuple
+//
+// Given the template parameter type `T` and a tuple of arguments
+// `std::tuple(arg0, arg1, ..., argN)` constructs an object of type `T` as if by
+// calling `T(arg0, arg1, ..., argN)`.
+//
+// Example:
+//
+//   std::tuple<const char*, size_t> args("hello world", 5);
+//   auto s = absl::make_from_tuple<std::string>(args);
+//   assert(s == "hello");
+//
+template <typename T, typename Tuple>
+constexpr T make_from_tuple(Tuple&& tup) {
+  return utility_internal::make_from_tuple_impl<T>(
+      std::forward<Tuple>(tup),
+      absl::make_index_sequence<
+          std::tuple_size<absl::decay_t<Tuple>>::value>{});
+}
+
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_UTILITY_UTILITY_H_