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authorGravatar Dino Radakovic <dinor@google.com>2022-06-16 16:42:34 -0700
committerGravatar Copybara-Service <copybara-worker@google.com>2022-06-16 16:43:07 -0700
commitb7ceff06d2358d09ba967c00f526b6143f207d56 (patch)
treec8350bffed0225834428b7b889b4b905ce350955 /absl/functional/internal
parent53a90f079af7ab491530d432bb318a95371ba877 (diff)
Release absl::AnyInvocable
AnyInvocable is a C++11 compatible equivalent of the C++23 [std::move_only_function](https://en.cppreference.com/w/cpp/utility/functional/move_only_function/move_only_function). Although this implementation matches an intermediate draft revision of the standard (http://wg21.link/p0288r5), it is neither a standard tracking type nor a seamless backfill type. PiperOrigin-RevId: 455494585 Change-Id: If01565f8eecc78eee38fb794ef142b32b31abc7c
Diffstat (limited to 'absl/functional/internal')
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diff --git a/absl/functional/internal/any_invocable.h b/absl/functional/internal/any_invocable.h
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+// 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 of the proposed `any_invocable` uses an approach that //
+// 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 <functional>
+#include <initializer_list>
+#include <memory>
+#include <new>
+#include <type_traits>
+#include <utility>
+
+#include "absl/base/config.h"
+#include "absl/base/internal/invoke.h"
+#include "absl/base/macros.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) {
+ return absl::base_internal::invoke(std::forward<F>(f),
+ std::forward<P>(args)...);
+}
+
+//
+////////////////////////////////////////////////////////////////////////////////
+
+////////////////////////////////////////////////////////////////////////////////
+///
+// 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 ABSL_INTERNAL_CPLUSPLUS_LANG >= 201703L
+ 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 ignored "-Wstrict-aliasing"
+#pragma GCC diagnostic push
+#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_INTERNAL_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_INTERNAL_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_INTERNAL_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 : int {
+ kPointer = 0,
+ kCompatibleAnyInvocable = 1,
+ kIncompatibleAnyInvocable = 2,
+ kOther = 3,
+ };
+
+ // 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<static_cast<int>(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/destory 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 <int target_type, class QualDecayedTRef, class F,
+ absl::enable_if_t<target_type == 0, 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 ignored "-Wpragmas"
+#pragma GCC diagnostic ignored "-Waddress"
+#pragma GCC diagnostic ignored "-Wnonnull-compare"
+#pragma GCC diagnostic push
+#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 <int target_type, class QualDecayedTRef, class F,
+ absl::enable_if_t<target_type == 1, 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 <int target_type, class QualDecayedTRef, class F,
+ absl::enable_if_t<target_type == 2, int> = 0>
+ void Initialize(F&& f) {
+ if (f.HasValue()) {
+ InitializeStorage<QualDecayedTRef>(std::forward<F>(f));
+ } else {
+ manager_ = EmptyManager;
+ invoker_ = nullptr;
+ }
+ }
+
+ template <int target_type, class QualDecayedTRef, class F,
+ typename = absl::enable_if_t<target_type == 3>>
+ 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 True =
+ 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 =
+ True<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 = True<
+ 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 =
+ True<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 =
+ True<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 = True<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 = \
+ True<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)...) {} \
+ \
+ /*The actual invocation operation with the proper signature*/ \
+ ReturnType operator()(P... args) cv ref noexcept(noex) { \
+ assert(this->invoker_ != nullptr); \
+ return this->invoker_(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_