// 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);

}

Unexecuted instantiation: unsigned int&& absl::lts_20230125::forward<unsigned int>(std::__1::remove_reference<unsigned int>::type&)

Unexecuted instantiation: absl::lts_20230125::string_view&& absl::lts_20230125::forward<absl::lts_20230125::string_view>(std::__1::remove_reference<absl::lts_20230125::string_view>::type&)

Unexecuted instantiation: char const*&& absl::lts_20230125::forward<char const*>(std::__1::remove_reference<char const*>::type&)

Unexecuted instantiation: absl::lts_20230125::container_internal::HashtablezInfoHandle&& absl::lts_20230125::forward<absl::lts_20230125::container_internal::HashtablezInfoHandle>(std::__1::remove_reference<absl::lts_20230125::container_internal::HashtablezInfoHandle>::type&)

Unexecuted instantiation: unsigned long& absl::lts_20230125::forward<unsigned long&>(std::__1::remove_reference<unsigned long&>::type&)

Unexecuted instantiation: void (*&&absl::lts_20230125::forward<void (*)(absl::lts_20230125::string_view)>(std::__1::remove_reference<void (*)(absl::lts_20230125::string_view)>::type&))(absl::lts_20230125::string_view)

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_