// Copyright 2022 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.

//

// Implementation details for `absl::AnyInvocable`

#ifndef ABSL_FUNCTIONAL_INTERNAL_ANY_INVOCABLE_H_

#define ABSL_FUNCTIONAL_INTERNAL_ANY_INVOCABLE_H_

////////////////////////////////////////////////////////////////////////////////

//                                                                            //

// This implementation chooses between local storage and remote storage for   //

// the contained target object based on the target object's size, alignment   //

// requirements, and whether or not it has a nothrow move constructor.        //

// Additional optimizations are performed when the object is a trivially      //

// copyable type [basic.types].                                               //

//                                                                            //

// There are three datamembers per `AnyInvocable` instance                    //

//                                                                            //

// 1) A union containing either                                               //

//        - A pointer to the target object referred to via a void*, or        //

//        - the target object, emplaced into a raw char buffer                //

//                                                                            //

// 2) A function pointer to a "manager" function operation that takes a       //

//    discriminator and logically branches to either perform a move operation //

//    or destroy operation based on that discriminator.                       //

//                                                                            //

// 3) A function pointer to an "invoker" function operation that invokes the  //

//    target object, directly returning the result.                           //

//                                                                            //

// When in the logically empty state, the manager function is an empty        //

// function and the invoker function is one that would be undefined behavior  //

// to call.                                                                   //

//                                                                            //

// An additional optimization is performed when converting from one           //

// AnyInvocable to another where only the noexcept specification and/or the   //

// cv/ref qualifiers of the function type differ. In these cases, the         //

// conversion works by "moving the guts", similar to if they were the same    //

// exact type, as opposed to having to perform an additional layer of         //

// wrapping through remote storage.                                           //

//                                                                            //

////////////////////////////////////////////////////////////////////////////////

// IWYU pragma: private, include "absl/functional/any_invocable.h"

#include <cassert>

#include <cstddef>

#include <cstring>

#include <exception>

#include <functional>

#include <memory>

#include <new>

#include <type_traits>

#include <utility>

#include "absl/base/attributes.h"

#include "absl/base/config.h"

#include "absl/base/internal/invoke.h"

#include "absl/base/macros.h"

#include "absl/base/optimization.h"

#include "absl/meta/type_traits.h"

#include "absl/utility/utility.h"

namespace absl {

ABSL_NAMESPACE_BEGIN

// Helper macro used to prevent spelling `noexcept` in language versions older

// than C++17, where it is not part of the type system, in order to avoid

// compilation failures and internal compiler errors.

#if ABSL_INTERNAL_CPLUSPLUS_LANG >= 201703L

#define ABSL_INTERNAL_NOEXCEPT_SPEC(noex) noexcept(noex)

#else

#define ABSL_INTERNAL_NOEXCEPT_SPEC(noex)

#endif

// Defined in functional/any_invocable.h

template <class Sig>

class AnyInvocable;

namespace internal_any_invocable {

// Constants relating to the small-object-storage for AnyInvocable

enum StorageProperty : std::size_t {

  kAlignment = alignof(std::max_align_t),  // The alignment of the storage

  kStorageSize = sizeof(void*) * 2         // The size of the storage

};

////////////////////////////////////////////////////////////////////////////////

//

// A metafunction for checking if a type is an AnyInvocable instantiation.

// This is used during conversion operations.

template <class T>

struct IsAnyInvocable : std::false_type {};

template <class Sig>

struct IsAnyInvocable<AnyInvocable<Sig>> : std::true_type {};

//

////////////////////////////////////////////////////////////////////////////////

// A type trait that tells us whether or not a target function type should be

// stored locally in the small object optimization storage

template <class T>

using IsStoredLocally = std::integral_constant<

    bool, sizeof(T) <= kStorageSize && alignof(T) <= kAlignment &&

              kAlignment % alignof(T) == 0 &&

              std::is_nothrow_move_constructible<T>::value>;

// An implementation of std::remove_cvref_t of C++20.

template <class T>

using RemoveCVRef =

    typename std::remove_cv<typename std::remove_reference<T>::type>::type;

////////////////////////////////////////////////////////////////////////////////

//

// An implementation of the C++ standard INVOKE<R> pseudo-macro, operation is

// equivalent to std::invoke except that it forces an implicit conversion to the

// specified return type. If "R" is void, the function is executed and the

// return value is simply ignored.

template <class ReturnType, class F, class... P,

          typename = absl::enable_if_t<std::is_void<ReturnType>::value>>

void InvokeR(F&& f, P&&... args) {

  absl::base_internal::invoke(std::forward<F>(f), std::forward<P>(args)...);

}

template <class ReturnType, class F, class... P,

          absl::enable_if_t<!std::is_void<ReturnType>::value, int> = 0>

ReturnType InvokeR(F&& f, P&&... args) {

  // GCC 12 has a false-positive -Wmaybe-uninitialized warning here.

#if ABSL_INTERNAL_HAVE_MIN_GNUC_VERSION(12, 0)

#pragma GCC diagnostic push

#pragma GCC diagnostic ignored "-Wmaybe-uninitialized"

#endif

  return absl::base_internal::invoke(std::forward<F>(f),

                                     std::forward<P>(args)...);

#if ABSL_INTERNAL_HAVE_MIN_GNUC_VERSION(12, 0)

#pragma GCC diagnostic pop

#endif

}

//

////////////////////////////////////////////////////////////////////////////////

////////////////////////////////////////////////////////////////////////////////

///

// A metafunction that takes a "T" corresponding to a parameter type of the

// user's specified function type, and yields the parameter type to use for the

// type-erased invoker. In order to prevent observable moves, this must be

// either a reference or, if the type is trivial, the original parameter type

// itself. Since the parameter type may be incomplete at the point that this

// metafunction is used, we can only do this optimization for scalar types

// rather than for any trivial type.

template <typename T>

T ForwardImpl(std::true_type);

template <typename T>

T&& ForwardImpl(std::false_type);

// NOTE: We deliberately use an intermediate struct instead of a direct alias,

// as a workaround for b/206991861 on MSVC versions < 1924.

template <class T>

struct ForwardedParameter {

  using type = decltype((

      ForwardImpl<T>)(std::integral_constant<bool,

                                             std::is_scalar<T>::value>()));

};

template <class T>

using ForwardedParameterType = typename ForwardedParameter<T>::type;

//

////////////////////////////////////////////////////////////////////////////////

// A discriminator when calling the "manager" function that describes operation

// type-erased operation should be invoked.

//

// "relocate_from_to" specifies that the manager should perform a move.

//

// "dispose" specifies that the manager should perform a destroy.

enum class FunctionToCall : bool { relocate_from_to, dispose };

// The portion of `AnyInvocable` state that contains either a pointer to the

// target object or the object itself in local storage

union TypeErasedState {

  struct {

    // A pointer to the type-erased object when remotely stored

    void* target;

    // The size of the object for `RemoteManagerTrivial`

    std::size_t size;

  } remote;

  // Local-storage for the type-erased object when small and trivial enough

  alignas(kAlignment) char storage[kStorageSize];

};

// A typed accessor for the object in `TypeErasedState` storage

template <class T>

T& ObjectInLocalStorage(TypeErasedState* const state) {

  // We launder here because the storage may be reused with the same type.

#if defined(__cpp_lib_launder) && __cpp_lib_launder >= 201606L

  return *std::launder(reinterpret_cast<T*>(&state->storage));

#elif ABSL_HAVE_BUILTIN(__builtin_launder)

  return *__builtin_launder(reinterpret_cast<T*>(&state->storage));

#else

  // When `std::launder` or equivalent are not available, we rely on undefined

  // behavior, which works as intended on Abseil's officially supported

  // platforms as of Q2 2022.

#if !defined(__clang__) && defined(__GNUC__)

#pragma GCC diagnostic push

#pragma GCC diagnostic ignored "-Wstrict-aliasing"

#endif

  return *reinterpret_cast<T*>(&state->storage);

#if !defined(__clang__) && defined(__GNUC__)

#pragma GCC diagnostic pop

#endif

#endif

}

// The type for functions issuing lifetime-related operations: move and dispose

// A pointer to such a function is contained in each `AnyInvocable` instance.

// NOTE: When specifying `FunctionToCall::`dispose, the same state must be

// passed as both "from" and "to".

using ManagerType = void(FunctionToCall /*operation*/,

                         TypeErasedState* /*from*/, TypeErasedState* /*to*/)

    ABSL_INTERNAL_NOEXCEPT_SPEC(true);

// The type for functions issuing the actual invocation of the object

// A pointer to such a function is contained in each AnyInvocable instance.

template <bool SigIsNoexcept, class ReturnType, class... P>

using InvokerType = ReturnType(TypeErasedState*, ForwardedParameterType<P>...)

    ABSL_INTERNAL_NOEXCEPT_SPEC(SigIsNoexcept);

// The manager that is used when AnyInvocable is empty

inline void EmptyManager(FunctionToCall /*operation*/,

                         TypeErasedState* /*from*/,

                         TypeErasedState* /*to*/) noexcept {}

// The manager that is used when a target function is in local storage and is

// a trivially copyable type.

inline void LocalManagerTrivial(FunctionToCall /*operation*/,

                                TypeErasedState* const from,

                                TypeErasedState* const to) noexcept {

  // This single statement without branching handles both possible operations.

  //

  // For FunctionToCall::dispose, "from" and "to" point to the same state, and

  // so this assignment logically would do nothing.

  //

  // Note: Correctness here relies on http://wg21.link/p0593, which has only

  // become standard in C++20, though implementations do not break it in

  // practice for earlier versions of C++.

  //

  // The correct way to do this without that paper is to first placement-new a

  // default-constructed T in "to->storage" prior to the memmove, but doing so

  // requires a different function to be created for each T that is stored

  // locally, which can cause unnecessary bloat and be less cache friendly.

  *to = *from;

  // Note: Because the type is trivially copyable, the destructor does not need

  // to be called ("trivially copyable" requires a trivial destructor).

}

// The manager that is used when a target function is in local storage and is

// not a trivially copyable type.

template <class T>

void LocalManagerNontrivial(FunctionToCall operation,

                            TypeErasedState* const from,

                            TypeErasedState* const to) noexcept {

  static_assert(IsStoredLocally<T>::value,

                "Local storage must only be used for supported types.");

  static_assert(!std::is_trivially_copyable<T>::value,

                "Locally stored types must be trivially copyable.");

  T& from_object = (ObjectInLocalStorage<T>)(from);

  switch (operation) {

    case FunctionToCall::relocate_from_to:

      // NOTE: Requires that the left-hand operand is already empty.

      ::new (static_cast<void*>(&to->storage)) T(std::move(from_object));

      ABSL_FALLTHROUGH_INTENDED;

    case FunctionToCall::dispose:

      from_object.~T();  // Must not throw. // NOLINT

      return;

  }

  ABSL_UNREACHABLE();

}

// The invoker that is used when a target function is in local storage

// Note: QualTRef here is the target function type along with cv and reference

// qualifiers that must be used when calling the function.

template <bool SigIsNoexcept, class ReturnType, class QualTRef, class... P>

ReturnType LocalInvoker(

    TypeErasedState* const state,

    ForwardedParameterType<P>... args) noexcept(SigIsNoexcept) {

  using RawT = RemoveCVRef<QualTRef>;

  static_assert(

      IsStoredLocally<RawT>::value,

      "Target object must be in local storage in order to be invoked from it.");

  auto& f = (ObjectInLocalStorage<RawT>)(state);

  return (InvokeR<ReturnType>)(static_cast<QualTRef>(f),

                               static_cast<ForwardedParameterType<P>>(args)...);

}

// The manager that is used when a target function is in remote storage and it

// has a trivial destructor

inline void RemoteManagerTrivial(FunctionToCall operation,

                                 TypeErasedState* const from,

                                 TypeErasedState* const to) noexcept {

  switch (operation) {

    case FunctionToCall::relocate_from_to:

      // NOTE: Requires that the left-hand operand is already empty.

      to->remote = from->remote;

      return;

    case FunctionToCall::dispose:

#if defined(__cpp_sized_deallocation)

      ::operator delete(from->remote.target, from->remote.size);

#else   // __cpp_sized_deallocation

      ::operator delete(from->remote.target);

#endif  // __cpp_sized_deallocation

      return;

  }

  ABSL_UNREACHABLE();

}

// The manager that is used when a target function is in remote storage and the

// destructor of the type is not trivial

template <class T>

void RemoteManagerNontrivial(FunctionToCall operation,

                             TypeErasedState* const from,

                             TypeErasedState* const to) noexcept {

  static_assert(!IsStoredLocally<T>::value,

                "Remote storage must only be used for types that do not "

                "qualify for local storage.");

  switch (operation) {

    case FunctionToCall::relocate_from_to:

      // NOTE: Requires that the left-hand operand is already empty.

      to->remote.target = from->remote.target;

      return;

    case FunctionToCall::dispose:

      ::delete static_cast<T*>(from->remote.target);  // Must not throw.

      return;

  }

  ABSL_UNREACHABLE();

}

// The invoker that is used when a target function is in remote storage

template <bool SigIsNoexcept, class ReturnType, class QualTRef, class... P>

ReturnType RemoteInvoker(

    TypeErasedState* const state,

    ForwardedParameterType<P>... args) noexcept(SigIsNoexcept) {

  using RawT = RemoveCVRef<QualTRef>;

  static_assert(!IsStoredLocally<RawT>::value,

                "Target object must be in remote storage in order to be "

                "invoked from it.");

  auto& f = *static_cast<RawT*>(state->remote.target);

  return (InvokeR<ReturnType>)(static_cast<QualTRef>(f),

                               static_cast<ForwardedParameterType<P>>(args)...);

}

////////////////////////////////////////////////////////////////////////////////

//

// A metafunction that checks if a type T is an instantiation of

// absl::in_place_type_t (needed for constructor constraints of AnyInvocable).

template <class T>

struct IsInPlaceType : std::false_type {};

template <class T>

struct IsInPlaceType<absl::in_place_type_t<T>> : std::true_type {};

//

////////////////////////////////////////////////////////////////////////////////

// A constructor name-tag used with CoreImpl (below) to request the

// conversion-constructor. QualDecayedTRef is the decayed-type of the object to

// wrap, along with the cv and reference qualifiers that must be applied when

// performing an invocation of the wrapped object.

template <class QualDecayedTRef>

struct TypedConversionConstruct {};

// A helper base class for all core operations of AnyInvocable. Most notably,

// this class creates the function call operator and constraint-checkers so that

// the top-level class does not have to be a series of partial specializations.

//

// Note: This definition exists (as opposed to being a declaration) so that if

// the user of the top-level template accidentally passes a template argument

// that is not a function type, they will get a static_assert in AnyInvocable's

// class body rather than an error stating that Impl is not defined.

template <class Sig>

class Impl {};  // Note: This is partially-specialized later.

// A std::unique_ptr deleter that deletes memory allocated via ::operator new.

#if defined(__cpp_sized_deallocation)

class TrivialDeleter {

 public:

  explicit TrivialDeleter(std::size_t size) : size_(size) {}

  void operator()(void* target) const {

    ::operator delete(target, size_);

  }

 private:

  std::size_t size_;

};

#else   // __cpp_sized_deallocation

class TrivialDeleter {

 public:

  explicit TrivialDeleter(std::size_t) {}

  void operator()(void* target) const { ::operator delete(target); }

};

#endif  // __cpp_sized_deallocation

template <bool SigIsNoexcept, class ReturnType, class... P>

class CoreImpl;

constexpr bool IsCompatibleConversion(void*, void*) { return false; }

template <bool NoExceptSrc, bool NoExceptDest, class... T>

constexpr bool IsCompatibleConversion(CoreImpl<NoExceptSrc, T...>*,

                                      CoreImpl<NoExceptDest, T...>*) {

  return !NoExceptDest || NoExceptSrc;

}

// A helper base class for all core operations of AnyInvocable that do not

// depend on the cv/ref qualifiers of the function type.

template <bool SigIsNoexcept, class ReturnType, class... P>

class CoreImpl {

 public:

  using result_type = ReturnType;

  CoreImpl() noexcept : manager_(EmptyManager), invoker_(nullptr) {}

  enum class TargetType {

    kPointer,

    kCompatibleAnyInvocable,

    kIncompatibleAnyInvocable,

    kOther,

  };

  // Note: QualDecayedTRef here includes the cv-ref qualifiers associated with

  // the invocation of the Invocable. The unqualified type is the target object

  // type to be stored.

  template <class QualDecayedTRef, class F>

  explicit CoreImpl(TypedConversionConstruct<QualDecayedTRef>, F&& f) {

    using DecayedT = RemoveCVRef<QualDecayedTRef>;

    constexpr TargetType kTargetType =

        (std::is_pointer<DecayedT>::value ||

         std::is_member_pointer<DecayedT>::value)

            ? TargetType::kPointer

        : IsCompatibleAnyInvocable<DecayedT>::value

            ? TargetType::kCompatibleAnyInvocable

        : IsAnyInvocable<DecayedT>::value

            ? TargetType::kIncompatibleAnyInvocable

            : TargetType::kOther;

    // NOTE: We only use integers instead of enums as template parameters in

    // order to work around a bug on C++14 under MSVC 2017.

    // See b/236131881.

    Initialize<kTargetType, QualDecayedTRef>(std::forward<F>(f));

  }

  // Note: QualTRef here includes the cv-ref qualifiers associated with the

  // invocation of the Invocable. The unqualified type is the target object

  // type to be stored.

  template <class QualTRef, class... Args>

  explicit CoreImpl(absl::in_place_type_t<QualTRef>, Args&&... args) {

    InitializeStorage<QualTRef>(std::forward<Args>(args)...);

  }

  CoreImpl(CoreImpl&& other) noexcept {

    other.manager_(FunctionToCall::relocate_from_to, &other.state_, &state_);

    manager_ = other.manager_;

    invoker_ = other.invoker_;

    other.manager_ = EmptyManager;

    other.invoker_ = nullptr;

  }

  CoreImpl& operator=(CoreImpl&& other) noexcept {

    // Put the left-hand operand in an empty state.

    //

    // Note: A full reset that leaves us with an object that has its invariants

    // intact is necessary in order to handle self-move. This is required by

    // types that are used with certain operations of the standard library, such

    // as the default definition of std::swap when both operands target the same

    // object.

    Clear();

    // Perform the actual move/destroy operation on the target function.

    other.manager_(FunctionToCall::relocate_from_to, &other.state_, &state_);

    manager_ = other.manager_;

    invoker_ = other.invoker_;

    other.manager_ = EmptyManager;

    other.invoker_ = nullptr;

    return *this;

  }

  ~CoreImpl() { manager_(FunctionToCall::dispose, &state_, &state_); }

  // Check whether or not the AnyInvocable is in the empty state.

  bool HasValue() const { return invoker_ != nullptr; }

  // Effects: Puts the object into its empty state.

  void Clear() {

    manager_(FunctionToCall::dispose, &state_, &state_);

    manager_ = EmptyManager;

    invoker_ = nullptr;

  }

  template <TargetType target_type, class QualDecayedTRef, class F,

            absl::enable_if_t<target_type == TargetType::kPointer, int> = 0>

  void Initialize(F&& f) {

// This condition handles types that decay into pointers, which includes

// function references. Since function references cannot be null, GCC warns

// against comparing their decayed form with nullptr.

// Since this is template-heavy code, we prefer to disable these warnings

// locally instead of adding yet another overload of this function.

#if !defined(__clang__) && defined(__GNUC__)

#pragma GCC diagnostic push

#pragma GCC diagnostic ignored "-Wpragmas"

#pragma GCC diagnostic ignored "-Waddress"

#pragma GCC diagnostic ignored "-Wnonnull-compare"

#endif

    if (static_cast<RemoveCVRef<QualDecayedTRef>>(f) == nullptr) {

#if !defined(__clang__) && defined(__GNUC__)

#pragma GCC diagnostic pop

#endif

      manager_ = EmptyManager;

      invoker_ = nullptr;

      return;

    }

    InitializeStorage<QualDecayedTRef>(std::forward<F>(f));

  }

  template <TargetType target_type, class QualDecayedTRef, class F,

            absl::enable_if_t<

                target_type == TargetType::kCompatibleAnyInvocable, int> = 0>

  void Initialize(F&& f) {

    // In this case we can "steal the guts" of the other AnyInvocable.

    f.manager_(FunctionToCall::relocate_from_to, &f.state_, &state_);

    manager_ = f.manager_;

    invoker_ = f.invoker_;

    f.manager_ = EmptyManager;

    f.invoker_ = nullptr;

  }

  template <TargetType target_type, class QualDecayedTRef, class F,

            absl::enable_if_t<

                target_type == TargetType::kIncompatibleAnyInvocable, int> = 0>

  void Initialize(F&& f) {

    if (f.HasValue()) {

      InitializeStorage<QualDecayedTRef>(std::forward<F>(f));

    } else {

      manager_ = EmptyManager;

      invoker_ = nullptr;

    }

  }

  template <TargetType target_type, class QualDecayedTRef, class F,

            typename = absl::enable_if_t<target_type == TargetType::kOther>>

  void Initialize(F&& f) {

    InitializeStorage<QualDecayedTRef>(std::forward<F>(f));

  }

  // Use local (inline) storage for applicable target object types.

  template <class QualTRef, class... Args,

            typename = absl::enable_if_t<

                IsStoredLocally<RemoveCVRef<QualTRef>>::value>>

  void InitializeStorage(Args&&... args) {

    using RawT = RemoveCVRef<QualTRef>;

    ::new (static_cast<void*>(&state_.storage))

        RawT(std::forward<Args>(args)...);

    invoker_ = LocalInvoker<SigIsNoexcept, ReturnType, QualTRef, P...>;

    // We can simplify our manager if we know the type is trivially copyable.

    InitializeLocalManager<RawT>();

  }

  // Use remote storage for target objects that cannot be stored locally.

  template <class QualTRef, class... Args,

            absl::enable_if_t<!IsStoredLocally<RemoveCVRef<QualTRef>>::value,

                              int> = 0>

  void InitializeStorage(Args&&... args) {

    InitializeRemoteManager<RemoveCVRef<QualTRef>>(std::forward<Args>(args)...);

    // This is set after everything else in case an exception is thrown in an

    // earlier step of the initialization.

    invoker_ = RemoteInvoker<SigIsNoexcept, ReturnType, QualTRef, P...>;

  }

  template <class T,

            typename = absl::enable_if_t<std::is_trivially_copyable<T>::value>>

  void InitializeLocalManager() {

    manager_ = LocalManagerTrivial;

  }

  template <class T,

            absl::enable_if_t<!std::is_trivially_copyable<T>::value, int> = 0>

  void InitializeLocalManager() {

    manager_ = LocalManagerNontrivial<T>;

  }

  template <class T>

  using HasTrivialRemoteStorage =

      std::integral_constant<bool, std::is_trivially_destructible<T>::value &&

                                       alignof(T) <=

                                           ABSL_INTERNAL_DEFAULT_NEW_ALIGNMENT>;

  template <class T, class... Args,

            typename = absl::enable_if_t<HasTrivialRemoteStorage<T>::value>>

  void InitializeRemoteManager(Args&&... args) {

    // unique_ptr is used for exception-safety in case construction throws.

    std::unique_ptr<void, TrivialDeleter> uninitialized_target(

        ::operator new(sizeof(T)), TrivialDeleter(sizeof(T)));

    ::new (uninitialized_target.get()) T(std::forward<Args>(args)...);

    state_.remote.target = uninitialized_target.release();

    state_.remote.size = sizeof(T);

    manager_ = RemoteManagerTrivial;

  }

  template <class T, class... Args,

            absl::enable_if_t<!HasTrivialRemoteStorage<T>::value, int> = 0>

  void InitializeRemoteManager(Args&&... args) {

    state_.remote.target = ::new T(std::forward<Args>(args)...);

    manager_ = RemoteManagerNontrivial<T>;

  }

  //////////////////////////////////////////////////////////////////////////////

  //

  // Type trait to determine if the template argument is an AnyInvocable whose

  // function type is compatible enough with ours such that we can

  // "move the guts" out of it when moving, rather than having to place a new

  // object into remote storage.

  template <typename Other>

  struct IsCompatibleAnyInvocable {

    static constexpr bool value = false;

  };

  template <typename Sig>

  struct IsCompatibleAnyInvocable<AnyInvocable<Sig>> {

    static constexpr bool value =

        (IsCompatibleConversion)(static_cast<

                                     typename AnyInvocable<Sig>::CoreImpl*>(

                                     nullptr),

                                 static_cast<CoreImpl*>(nullptr));

  };

  //

  //////////////////////////////////////////////////////////////////////////////

  TypeErasedState state_;

  ManagerType* manager_;

  InvokerType<SigIsNoexcept, ReturnType, P...>* invoker_;

};

// A constructor name-tag used with Impl to request the

// conversion-constructor

struct ConversionConstruct {};

////////////////////////////////////////////////////////////////////////////////

//

// A metafunction that is normally an identity metafunction except that when

// given a std::reference_wrapper<T>, it yields T&. This is necessary because

// currently std::reference_wrapper's operator() is not conditionally noexcept,

// so when checking if such an Invocable is nothrow-invocable, we must pull out

// the underlying type.

template <class T>

struct UnwrapStdReferenceWrapperImpl {

  using type = T;

};

template <class T>

struct UnwrapStdReferenceWrapperImpl<std::reference_wrapper<T>> {

  using type = T&;

};

template <class T>

using UnwrapStdReferenceWrapper =

    typename UnwrapStdReferenceWrapperImpl<T>::type;

//

////////////////////////////////////////////////////////////////////////////////

// An alias that always yields std::true_type (used with constraints) where

// substitution failures happen when forming the template arguments.

template <class... T>

using TrueAlias =

    std::integral_constant<bool, sizeof(absl::void_t<T...>*) != 0>;

/*SFINAE constraints for the conversion-constructor.*/

template <class Sig, class F,

          class = absl::enable_if_t<

              !std::is_same<RemoveCVRef<F>, AnyInvocable<Sig>>::value>>

using CanConvert = TrueAlias<

    absl::enable_if_t<!IsInPlaceType<RemoveCVRef<F>>::value>,

    absl::enable_if_t<Impl<Sig>::template CallIsValid<F>::value>,

    absl::enable_if_t<

        Impl<Sig>::template CallIsNoexceptIfSigIsNoexcept<F>::value>,

    absl::enable_if_t<std::is_constructible<absl::decay_t<F>, F>::value>>;

/*SFINAE constraints for the std::in_place constructors.*/

template <class Sig, class F, class... Args>

using CanEmplace = TrueAlias<

    absl::enable_if_t<Impl<Sig>::template CallIsValid<F>::value>,

    absl::enable_if_t<

        Impl<Sig>::template CallIsNoexceptIfSigIsNoexcept<F>::value>,

    absl::enable_if_t<std::is_constructible<absl::decay_t<F>, Args...>::value>>;

/*SFINAE constraints for the conversion-assign operator.*/

template <class Sig, class F,

          class = absl::enable_if_t<

              !std::is_same<RemoveCVRef<F>, AnyInvocable<Sig>>::value>>

using CanAssign = TrueAlias<

    absl::enable_if_t<Impl<Sig>::template CallIsValid<F>::value>,

    absl::enable_if_t<

        Impl<Sig>::template CallIsNoexceptIfSigIsNoexcept<F>::value>,

    absl::enable_if_t<std::is_constructible<absl::decay_t<F>, F>::value>>;

/*SFINAE constraints for the reference-wrapper conversion-assign operator.*/

template <class Sig, class F>

using CanAssignReferenceWrapper = TrueAlias<

    absl::enable_if_t<

        Impl<Sig>::template CallIsValid<std::reference_wrapper<F>>::value>,

    absl::enable_if_t<Impl<Sig>::template CallIsNoexceptIfSigIsNoexcept<

        std::reference_wrapper<F>>::value>>;

////////////////////////////////////////////////////////////////////////////////

//

// The constraint for checking whether or not a call meets the noexcept

// callability requirements. This is a preprocessor macro because specifying it

// this way as opposed to a disjunction/branch can improve the user-side error

// messages and avoids an instantiation of std::is_nothrow_invocable_r in the

// cases where the user did not specify a noexcept function type.

//

#define ABSL_INTERNAL_ANY_INVOCABLE_NOEXCEPT_CONSTRAINT(inv_quals, noex) \

  ABSL_INTERNAL_ANY_INVOCABLE_NOEXCEPT_CONSTRAINT_##noex(inv_quals)

// The disjunction below is because we can't rely on std::is_nothrow_invocable_r

// to give the right result when ReturnType is non-moveable in toolchains that

// don't treat non-moveable result types correctly. For example this was the

// case in libc++ before commit c3a24882 (2022-05).

#define ABSL_INTERNAL_ANY_INVOCABLE_NOEXCEPT_CONSTRAINT_true(inv_quals)      \

  absl::enable_if_t<absl::disjunction<                                       \

      std::is_nothrow_invocable_r<                                           \

          ReturnType, UnwrapStdReferenceWrapper<absl::decay_t<F>> inv_quals, \

          P...>,                                                             \

      std::conjunction<                                                      \

          std::is_nothrow_invocable<                                         \

              UnwrapStdReferenceWrapper<absl::decay_t<F>> inv_quals, P...>,  \

          std::is_same<                                                      \

              ReturnType,                                                    \

              absl::base_internal::invoke_result_t<                          \

                  UnwrapStdReferenceWrapper<absl::decay_t<F>> inv_quals,     \

                  P...>>>>::value>

#define ABSL_INTERNAL_ANY_INVOCABLE_NOEXCEPT_CONSTRAINT_false(inv_quals)

//

////////////////////////////////////////////////////////////////////////////////

// A macro to generate partial specializations of Impl with the different

// combinations of supported cv/reference qualifiers and noexcept specifier.

//

// Here, `cv` are the cv-qualifiers if any, `ref` is the ref-qualifier if any,

// inv_quals is the reference type to be used when invoking the target, and

// noex is "true" if the function type is noexcept, or false if it is not.

//

// The CallIsValid condition is more complicated than simply using

// absl::base_internal::is_invocable_r because we can't rely on it to give the

// right result when ReturnType is non-moveable in toolchains that don't treat

// non-moveable result types correctly. For example this was the case in libc++

// before commit c3a24882 (2022-05).

#define ABSL_INTERNAL_ANY_INVOCABLE_IMPL_(cv, ref, inv_quals, noex)            \

  template <class ReturnType, class... P>                                      \

  class Impl<ReturnType(P...) cv ref ABSL_INTERNAL_NOEXCEPT_SPEC(noex)>        \

      : public CoreImpl<noex, ReturnType, P...> {                              \

   public:                                                                     \

    /*The base class, which contains the datamembers and core operations*/     \

    using Core = CoreImpl<noex, ReturnType, P...>;                             \

                                                                               \

    /*SFINAE constraint to check if F is invocable with the proper signature*/ \

    template <class F>                                                         \

    using CallIsValid = TrueAlias<absl::enable_if_t<absl::disjunction<         \

        absl::base_internal::is_invocable_r<ReturnType,                        \

                                            absl::decay_t<F> inv_quals, P...>, \

        std::is_same<ReturnType,                                               \

                     absl::base_internal::invoke_result_t<                     \

                         absl::decay_t<F> inv_quals, P...>>>::value>>;         \

                                                                               \

    /*SFINAE constraint to check if F is nothrow-invocable when necessary*/    \

    template <class F>                                                         \

    using CallIsNoexceptIfSigIsNoexcept =                                      \

        TrueAlias<ABSL_INTERNAL_ANY_INVOCABLE_NOEXCEPT_CONSTRAINT(inv_quals,   \

                                                                  noex)>;      \

                                                                               \

    /*Put the AnyInvocable into an empty state.*/                              \

    Impl() = default;                                                          \

                                                                               \

    /*The implementation of a conversion-constructor from "f*/                 \

    /*This forwards to Core, attaching inv_quals so that the base class*/      \

    /*knows how to properly type-erase the invocation.*/                       \

    template <class F>                                                         \

    explicit Impl(ConversionConstruct, F&& f)                                  \

        : Core(TypedConversionConstruct<                                       \

                   typename std::decay<F>::type inv_quals>(),                  \

               std::forward<F>(f)) {}                                          \

                                                                               \

    /*Forward along the in-place construction parameters.*/                    \

    template <class T, class... Args>                                          \

    explicit Impl(absl::in_place_type_t<T>, Args&&... args)                    \

        : Core(absl::in_place_type<absl::decay_t<T> inv_quals>,                \

               std::forward<Args>(args)...) {}                                 \

                                                                               \

    /*Raises a fatal error when the AnyInvocable is invoked after a move*/     \

    static ReturnType InvokedAfterMove(                                        \

      TypeErasedState*,                                                        \

      ForwardedParameterType<P>...) noexcept(noex) {                           \

      ABSL_HARDENING_ASSERT(false && "AnyInvocable use-after-move");           \

      std::terminate();                                                        \

    }                                                                          \

                                                                               \

    InvokerType<noex, ReturnType, P...>* ExtractInvoker() cv {                 \

      using QualifiedTestType = int cv ref;                                    \

      auto* invoker = this->invoker_;                                          \

      if (!std::is_const<QualifiedTestType>::value &&                          \

          std::is_rvalue_reference<QualifiedTestType>::value) {                \

        ABSL_ASSERT([this]() {                                                 \

          /* We checked that this isn't const above, so const_cast is safe */  \

          const_cast<Impl*>(this)->invoker_ = InvokedAfterMove;                \

          return this->HasValue();                                             \

        }());                                                                  \

      }                                                                        \

      return invoker;                                                          \

    }                                                                          \

                                                                               \

    /*The actual invocation operation with the proper signature*/              \

    ReturnType operator()(P... args) cv ref noexcept(noex) {                   \

      assert(this->invoker_ != nullptr);                                       \

      return this->ExtractInvoker()(                                           \

          const_cast<TypeErasedState*>(&this->state_),                         \

          static_cast<ForwardedParameterType<P>>(args)...);                    \

    }                                                                          \

  }

// Define the `noexcept(true)` specialization only for C++17 and beyond, when

// `noexcept` is part of the type system.

#if ABSL_INTERNAL_CPLUSPLUS_LANG >= 201703L

// A convenience macro that defines specializations for the noexcept(true) and

// noexcept(false) forms, given the other properties.

#define ABSL_INTERNAL_ANY_INVOCABLE_IMPL(cv, ref, inv_quals)    \

  ABSL_INTERNAL_ANY_INVOCABLE_IMPL_(cv, ref, inv_quals, false); \

  ABSL_INTERNAL_ANY_INVOCABLE_IMPL_(cv, ref, inv_quals, true)

#else

#define ABSL_INTERNAL_ANY_INVOCABLE_IMPL(cv, ref, inv_quals) \

  ABSL_INTERNAL_ANY_INVOCABLE_IMPL_(cv, ref, inv_quals, false)

#endif

// Non-ref-qualified partial specializations

ABSL_INTERNAL_ANY_INVOCABLE_IMPL(, , &);

ABSL_INTERNAL_ANY_INVOCABLE_IMPL(const, , const&);

// Lvalue-ref-qualified partial specializations

ABSL_INTERNAL_ANY_INVOCABLE_IMPL(, &, &);

ABSL_INTERNAL_ANY_INVOCABLE_IMPL(const, &, const&);

// Rvalue-ref-qualified partial specializations

ABSL_INTERNAL_ANY_INVOCABLE_IMPL(, &&, &&);

ABSL_INTERNAL_ANY_INVOCABLE_IMPL(const, &&, const&&);

// Undef the detail-only macros.

#undef ABSL_INTERNAL_ANY_INVOCABLE_IMPL

#undef ABSL_INTERNAL_ANY_INVOCABLE_IMPL_

#undef ABSL_INTERNAL_ANY_INVOCABLE_NOEXCEPT_CONSTRAINT_false

#undef ABSL_INTERNAL_ANY_INVOCABLE_NOEXCEPT_CONSTRAINT_true

#undef ABSL_INTERNAL_ANY_INVOCABLE_NOEXCEPT_CONSTRAINT

#undef ABSL_INTERNAL_NOEXCEPT_SPEC

}  // namespace internal_any_invocable

ABSL_NAMESPACE_END

}  // namespace absl

#endif  // ABSL_FUNCTIONAL_INTERNAL_ANY_INVOCABLE_H_