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diff --git a/absl/functional/internal/any_invocable.h b/absl/functional/internal/any_invocable.h new file mode 100644 index 00000000..f353139c --- /dev/null +++ b/absl/functional/internal/any_invocable.h @@ -0,0 +1,857 @@ +// 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_ |