#include <utility>
#include <folly/CppAttributes.h>
+#include <folly/Portability.h>
namespace folly {
-namespace impl {
-template <typename FunctionType, bool Const = false>
+template <typename FunctionType>
class Function;
template <typename ReturnType, typename... Args>
-Function<ReturnType(Args...), true> constCastFunction(
- Function<ReturnType(Args...), false>&&) noexcept;
-}
+Function<ReturnType(Args...) const> constCastFunction(
+ Function<ReturnType(Args...)>&&) noexcept;
namespace detail {
namespace function {
union Data {
void* big;
- typename std::aligned_storage<6 * sizeof(void*)>::type small;
+ std::aligned_storage<6 * sizeof(void*)>::type tiny;
};
-struct Tag {};
-
-template <bool If, typename T>
-using ConstIf = typename std::conditional<If, const T, T>::type;
-
template <typename Fun, typename FunT = typename std::decay<Fun>::type>
using IsSmall = std::integral_constant<
bool,
- (sizeof(FunT) <= sizeof(Data::small) &&
-#if defined(__GNUC__) && !defined(__clang__)
- // GCC has a name mangling bug that causes hard errors if we use noexcept
- // directly here. Last tested at gcc 5.3.0.
- // See: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70790
- std::is_nothrow_move_constructible<FunT>::value
-#else
+ (sizeof(FunT) <= sizeof(Data::tiny) &&
// Same as is_nothrow_move_constructible, but w/ no template instantiation.
- noexcept(FunT(std::declval<FunT&&>()))
-#endif
- )>;
+ noexcept(FunT(std::declval<FunT&&>())))>;
+using SmallTag = std::true_type;
+using HeapTag = std::false_type;
+
+struct CoerceTag {};
template <typename T>
bool isNullPtrFn(T* p) {
return {};
}
-template <typename ReturnType, typename... Args>
-ReturnType uninitCall(Data&, Args&&...) {
- throw std::bad_function_call();
-}
inline bool uninitNoop(Op, Data*, Data*) {
return false;
}
+
+template <typename FunctionType>
+struct FunctionTraits;
+
+template <typename ReturnType, typename... Args>
+struct FunctionTraits<ReturnType(Args...)> {
+ using Call = ReturnType (*)(Data&, Args&&...);
+ using IsConst = std::false_type;
+ using ConstSignature = ReturnType(Args...) const;
+ using NonConstSignature = ReturnType(Args...);
+ using OtherSignature = ConstSignature;
+
+ template <typename F, typename G = typename std::decay<F>::type>
+ using ResultOf = decltype(
+ static_cast<ReturnType>(std::declval<G&>()(std::declval<Args>()...)));
+
+ template <typename Fun>
+ static ReturnType callSmall(Data& p, Args&&... args) {
+ return static_cast<ReturnType>((*static_cast<Fun*>(
+ static_cast<void*>(&p.tiny)))(static_cast<Args&&>(args)...));
+ }
+
+ template <typename Fun>
+ static ReturnType callBig(Data& p, Args&&... args) {
+ return static_cast<ReturnType>(
+ (*static_cast<Fun*>(p.big))(static_cast<Args&&>(args)...));
+ }
+
+ static ReturnType uninitCall(Data&, Args&&...) {
+ throw std::bad_function_call();
+ }
+
+ ReturnType operator()(Args... args) {
+ auto& fn = *static_cast<Function<ReturnType(Args...)>*>(this);
+ return fn.call_(fn.data_, static_cast<Args&&>(args)...);
+ }
+
+ struct SharedFunctionImpl {
+ std::shared_ptr<Function<ReturnType(Args...)>> sp_;
+ ReturnType operator()(Args&&... args) const {
+ return (*sp_)(static_cast<Args&&>(args)...);
+ }
+ };
+};
+
+template <typename ReturnType, typename... Args>
+struct FunctionTraits<ReturnType(Args...) const> {
+ using Call = ReturnType (*)(Data&, Args&&...);
+ using IsConst = std::true_type;
+ using ConstSignature = ReturnType(Args...) const;
+ using NonConstSignature = ReturnType(Args...);
+ using OtherSignature = NonConstSignature;
+
+ template <typename F, typename G = typename std::decay<F>::type>
+ using ResultOf = decltype(static_cast<ReturnType>(
+ std::declval<const G&>()(std::declval<Args>()...)));
+
+ template <typename Fun>
+ static ReturnType callSmall(Data& p, Args&&... args) {
+ return static_cast<ReturnType>((*static_cast<const Fun*>(
+ static_cast<void*>(&p.tiny)))(static_cast<Args&&>(args)...));
+ }
+
+ template <typename Fun>
+ static ReturnType callBig(Data& p, Args&&... args) {
+ return static_cast<ReturnType>(
+ (*static_cast<const Fun*>(p.big))(static_cast<Args&&>(args)...));
+ }
+
+ static ReturnType uninitCall(Data&, Args&&...) {
+ throw std::bad_function_call();
+ }
+
+ ReturnType operator()(Args... args) const {
+ auto& fn = *static_cast<const Function<ReturnType(Args...) const>*>(this);
+ return fn.call_(fn.data_, static_cast<Args&&>(args)...);
+ }
+
+ struct SharedFunctionImpl {
+ std::shared_ptr<Function<ReturnType(Args...) const>> sp_;
+ ReturnType operator()(Args&&... args) const {
+ return (*sp_)(static_cast<Args&&>(args)...);
+ }
+ };
+};
+
+template <typename Fun>
+bool execSmall(Op o, Data* src, Data* dst) {
+ switch (o) {
+ case Op::MOVE:
+ ::new (static_cast<void*>(&dst->tiny))
+ Fun(std::move(*static_cast<Fun*>(static_cast<void*>(&src->tiny))));
+ FOLLY_FALLTHROUGH;
+ case Op::NUKE:
+ static_cast<Fun*>(static_cast<void*>(&src->tiny))->~Fun();
+ break;
+ case Op::FULL:
+ return true;
+ case Op::HEAP:
+ break;
+ }
+ return false;
+}
+
+template <typename Fun>
+bool execBig(Op o, Data* src, Data* dst) {
+ switch (o) {
+ case Op::MOVE:
+ dst->big = src->big;
+ src->big = nullptr;
+ break;
+ case Op::NUKE:
+ delete static_cast<Fun*>(src->big);
+ break;
+ case Op::FULL:
+ case Op::HEAP:
+ break;
+ }
+ return true;
+}
+
+// Invoke helper
+template <typename F, typename... Args>
+inline auto invoke(F&& f, Args&&... args)
+ -> decltype(std::forward<F>(f)(std::forward<Args>(args)...)) {
+ return std::forward<F>(f)(std::forward<Args>(args)...);
+}
+
+template <typename M, typename C, typename... Args>
+inline auto invoke(M(C::*d), Args&&... args)
+ -> decltype(std::mem_fn(d)(std::forward<Args>(args)...)) {
+ return std::mem_fn(d)(std::forward<Args>(args)...);
+}
+
} // namespace function
} // namespace detail
-namespace impl {
-
-template <typename ReturnType, typename... Args, bool Const>
-class Function<ReturnType(Args...), Const> final {
+FOLLY_PUSH_WARNING
+FOLLY_MSVC_DISABLE_WARNING(4521) // Multiple copy constructors
+FOLLY_MSVC_DISABLE_WARNING(4522) // Multiple assignment operators
+template <typename FunctionType>
+class Function final : private detail::function::FunctionTraits<FunctionType> {
+ // These utility types are defined outside of the template to reduce
+ // the number of instantiations, and then imported in the class
+ // namespace for convenience.
using Data = detail::function::Data;
using Op = detail::function::Op;
- using Tag = detail::function::Tag;
- using Call = ReturnType (*)(Data&, Args&&...);
+ using SmallTag = detail::function::SmallTag;
+ using HeapTag = detail::function::HeapTag;
+ using CoerceTag = detail::function::CoerceTag;
+
+ using Traits = detail::function::FunctionTraits<FunctionType>;
+ using Call = typename Traits::Call;
using Exec = bool (*)(Op, Data*, Data*);
- template <typename T>
- using ConstIf = detail::function::ConstIf<Const, T>;
template <typename Fun>
using IsSmall = detail::function::IsSmall<Fun>;
- Data data_;
- Call call_;
- Exec exec_;
-
- friend Function<ReturnType(Args...), true> constCastFunction<>(
- Function<ReturnType(Args...), false>&&) noexcept;
- friend class Function<ReturnType(Args...), !Const>;
-
- template <typename Fun, typename FunT = typename std::decay<Fun>::type>
- Function(
- Fun&& fun,
- typename std::enable_if<IsSmall<Fun>::value, Tag>::
- type) noexcept(noexcept(FunT(std::declval<Fun>())))
- : Function() {
- struct Ops {
- static ReturnType call(Data& p, Args&&... args) {
- return static_cast<ReturnType>((*static_cast<ConstIf<FunT>*>(
- (void*)&p.small))(static_cast<Args&&>(args)...));
- }
- static bool exec(Op o, Data* src, Data* dst) {
- switch (o) {
- case Op::MOVE:
- ::new ((void*)&dst->small)
- FunT(std::move(*static_cast<FunT*>((void*)&src->small)));
- FOLLY_FALLTHROUGH;
- case Op::NUKE:
- static_cast<FunT*>((void*)&src->small)->~FunT();
- break;
- case Op::FULL:
- return true;
- case Op::HEAP:
- break;
- }
- return false;
- }
- };
+ using OtherSignature = typename Traits::OtherSignature;
+
+ // The `data_` member is mutable to allow `constCastFunction` to work without
+ // invoking undefined behavior. Const-correctness is only violated when
+ // `FunctionType` is a const function type (e.g., `int() const`) and `*this`
+ // is the result of calling `constCastFunction`.
+ mutable Data data_;
+ Call call_{&Traits::uninitCall};
+ Exec exec_{&detail::function::uninitNoop};
+
+ friend Traits;
+ friend Function<typename Traits::ConstSignature> folly::constCastFunction<>(
+ Function<typename Traits::NonConstSignature>&&) noexcept;
+ friend class Function<OtherSignature>;
+
+ template <typename Fun>
+ Function(Fun&& fun, SmallTag) noexcept {
+ using FunT = typename std::decay<Fun>::type;
if (!detail::function::isNullPtrFn(fun)) {
- ::new (&data_.small) FunT(static_cast<Fun&&>(fun));
- exec_ = &Ops::exec;
- call_ = &Ops::call;
+ ::new (static_cast<void*>(&data_.tiny)) FunT(static_cast<Fun&&>(fun));
+ call_ = &Traits::template callSmall<FunT>;
+ exec_ = &detail::function::execSmall<FunT>;
}
}
- template <typename Fun, typename FunT = typename std::decay<Fun>::type>
- Function(Fun&& fun, typename std::enable_if<!IsSmall<Fun>::value, Tag>::type)
- : Function() {
- struct Ops {
- static ReturnType call(Data& p, Args&&... args) {
- return static_cast<ReturnType>((*static_cast<ConstIf<FunT>*>(p.big))(
- static_cast<Args&&>(args)...));
- }
- static bool exec(Op o, Data* src, Data* dst) {
- switch (o) {
- case Op::MOVE:
- dst->big = src->big;
- src->big = nullptr;
- break;
- case Op::NUKE:
- delete static_cast<FunT*>(src->big);
- break;
- case Op::FULL:
- case Op::HEAP:
- break;
- }
- return true;
- }
- };
+ template <typename Fun>
+ Function(Fun&& fun, HeapTag) {
+ using FunT = typename std::decay<Fun>::type;
data_.big = new FunT(static_cast<Fun&&>(fun));
- call_ = &Ops::call;
- exec_ = &Ops::exec;
+ call_ = &Traits::template callBig<FunT>;
+ exec_ = &detail::function::execBig<FunT>;
+ }
+
+ Function(Function<OtherSignature>&& that, CoerceTag) noexcept {
+ that.exec_(Op::MOVE, &that.data_, &data_);
+ std::swap(call_, that.call_);
+ std::swap(exec_, that.exec_);
}
- template <typename F, typename G = typename std::decay<F>::type>
- using ResultOf = decltype(static_cast<ReturnType>(
- std::declval<ConstIf<G>&>()(std::declval<Args>()...)));
public:
/**
* Default constructor. Constructs an empty Function.
*/
- Function() noexcept
- : call_(&detail::function::uninitCall<ReturnType, Args...>),
- exec_(&detail::function::uninitNoop) {}
+ Function() = default;
// not copyable
// NOTE: Deleting the non-const copy constructor is unusual but necessary to
// (i.e., `template <typename Fun> Function(Fun&&)`).
Function(Function&) = delete;
Function(const Function&) = delete;
+ Function(const Function&&) = delete;
/**
* Move constructor
*/
- Function(Function&& that) noexcept : Function() {
+ Function(Function&& that) noexcept {
that.exec_(Op::MOVE, &that.data_, &data_);
std::swap(call_, that.call_);
std::swap(exec_, that.exec_);
/**
* Constructs an empty `Function`.
*/
- /* implicit */ Function(std::nullptr_t) noexcept : Function() {}
+ /* implicit */ Function(std::nullptr_t) noexcept {}
/**
* Constructs a new `Function` from any callable object. This
* \note `typename = ResultOf<Fun>` prevents this overload from being
* selected by overload resolution when `fun` is not a compatible function.
*/
- template <class Fun, typename = ResultOf<Fun>>
- /* implicit */ Function(Fun&& fun) noexcept(
- noexcept(Function(std::declval<Fun>(), Tag{})))
- : Function(static_cast<Fun&&>(fun), Tag{}) {}
+ template <class Fun, typename = typename Traits::template ResultOf<Fun>>
+ /* implicit */ Function(Fun&& fun) noexcept(IsSmall<Fun>::value)
+ : Function(static_cast<Fun&&>(fun), IsSmall<Fun>{}) {}
/**
* For moving a `Function<X(Ys..) const>` into a `Function<X(Ys...)>`.
*/
template <
- bool OtherConst,
- typename std::enable_if<!Const && OtherConst, int>::type = 0>
- Function(Function<ReturnType(Args...), OtherConst>&& that) noexcept
- : Function() {
- that.exec_(Op::MOVE, &that.data_, &data_);
- std::swap(call_, that.call_);
- std::swap(exec_, that.exec_);
- }
+ bool Const = Traits::IsConst::value,
+ typename std::enable_if<!Const, int>::type = 0>
+ Function(Function<OtherSignature>&& that) noexcept
+ : Function(std::move(that), CoerceTag{}) {}
/**
* If `ptr` is null, constructs an empty `Function`. Otherwise,
// Prevent this overload from being selected when `ptr` is not a
// compatible member function pointer.
typename = decltype(Function(std::mem_fn((Member Class::*)0)))>
- /* implicit */ Function(Member Class::*ptr) noexcept : Function() {
+ /* implicit */ Function(Member Class::*ptr) noexcept {
if (ptr) {
*this = std::mem_fn(ptr);
}
* \note `typename = ResultOf<Fun>` prevents this overload from being
* selected by overload resolution when `fun` is not a compatible function.
*/
- template <class Fun, typename = ResultOf<Fun>>
+ template <class Fun, typename = typename Traits::template ResultOf<Fun>>
Function& operator=(Fun&& fun) noexcept(
noexcept(/* implicit */ Function(std::declval<Fun>()))) {
// Doing this in place is more efficient when we can do so safely.
/**
* Call the wrapped callable object with the specified arguments.
- * If this `Function` object is a const `folly::Function` object,
- * this overload shall not participate in overload resolution.
*/
- template <
- // `True` makes `operator()` a template so we can SFINAE on `Const`,
- // which is non-deduced here.
- bool True = true,
- typename std::enable_if<True && !Const, int>::type = 0>
- ReturnType operator()(Args... args) {
- return call_(data_, static_cast<Args&&>(args)...);
- }
-
- /**
- * Call the wrapped callable object with the specified arguments.
- * If this `Function` object is not a const `folly::Function` object,
- * this overload shall not participate in overload resolution.
- */
- template <
- // `True` makes `operator()` a template so we can SFINAE on `Const`,
- // which is non-deduced here.
- bool True = true,
- typename std::enable_if<True && Const, int>::type = 0>
- ReturnType operator()(Args... args) const {
- return call_(const_cast<Data&>(data_), static_cast<Args&&>(args)...);
- }
+ using Traits::operator();
/**
* Exchanges the callable objects of `*this` and `that`.
* Note that the returned `std::function` will share its state (i.e. captured
* data) across all copies you make of it, so be very careful when copying.
*/
- std::function<ReturnType(Args...)> asStdFunction() && {
- struct Impl {
- std::shared_ptr<Function> sp_;
- ReturnType operator()(Args&&... args) const {
- return (*sp_)(static_cast<Args&&>(args)...);
- }
- };
+ std::function<typename Traits::NonConstSignature> asStdFunction() && {
+ using Impl = typename Traits::SharedFunctionImpl;
return Impl{std::make_shared<Function>(std::move(*this))};
}
};
+FOLLY_POP_WARNING
-template <typename FunctionType, bool Const>
-void swap(
- Function<FunctionType, Const>& lhs,
- Function<FunctionType, Const>& rhs) noexcept {
+template <typename FunctionType>
+void swap(Function<FunctionType>& lhs, Function<FunctionType>& rhs) noexcept {
lhs.swap(rhs);
}
-template <typename FunctionType, bool Const>
-bool operator==(const Function<FunctionType, Const>& fn, std::nullptr_t) {
+template <typename FunctionType>
+bool operator==(const Function<FunctionType>& fn, std::nullptr_t) {
return !fn;
}
-template <typename FunctionType, bool Const>
-bool operator==(std::nullptr_t, const Function<FunctionType, Const>& fn) {
+template <typename FunctionType>
+bool operator==(std::nullptr_t, const Function<FunctionType>& fn) {
return !fn;
}
-template <typename FunctionType, bool Const>
-bool operator!=(const Function<FunctionType, Const>& fn, std::nullptr_t) {
+template <typename FunctionType>
+bool operator!=(const Function<FunctionType>& fn, std::nullptr_t) {
return !(fn == nullptr);
}
-template <typename FunctionType, bool Const>
-bool operator!=(std::nullptr_t, const Function<FunctionType, Const>& fn) {
+template <typename FunctionType>
+bool operator!=(std::nullptr_t, const Function<FunctionType>& fn) {
return !(nullptr == fn);
}
+/**
+ * NOTE: See detailed note about `constCastFunction` at the top of the file.
+ * This is potentially dangerous and requires the equivalent of a `const_cast`.
+ */
template <typename ReturnType, typename... Args>
-Function<ReturnType(Args...), true> constCastFunction(
- Function<ReturnType(Args...), false>&& that) noexcept {
- Function<ReturnType(Args...), true> fn{};
- that.exec_(detail::function::Op::MOVE, &that.data_, &fn.data_);
- std::swap(fn.call_, that.call_);
- std::swap(fn.exec_, that.exec_);
- return fn;
+Function<ReturnType(Args...) const> constCastFunction(
+ Function<ReturnType(Args...)>&& that) noexcept {
+ return Function<ReturnType(Args...) const>{std::move(that),
+ detail::function::CoerceTag{}};
}
-template <typename FunctionType>
-Function<FunctionType, true> constCastFunction(
- Function<FunctionType, true>&& that) noexcept {
+template <typename ReturnType, typename... Args>
+Function<ReturnType(Args...) const> constCastFunction(
+ Function<ReturnType(Args...) const>&& that) noexcept {
return std::move(that);
}
+/**
+ * @class FunctionRef
+ *
+ * @brief A reference wrapper for callable objects
+ *
+ * FunctionRef is similar to std::reference_wrapper, but the template parameter
+ * is the function signature type rather than the type of the referenced object.
+ * A folly::FunctionRef is cheap to construct as it contains only a pointer to
+ * the referenced callable and a pointer to a function which invokes the
+ * callable.
+ *
+ * The user of FunctionRef must be aware of the reference semantics: storing a
+ * copy of a FunctionRef is potentially dangerous and should be avoided unless
+ * the referenced object definitely outlives the FunctionRef object. Thus any
+ * function that accepts a FunctionRef parameter should only use it to invoke
+ * the referenced function and not store a copy of it. Knowing that FunctionRef
+ * itself has reference semantics, it is generally okay to use it to reference
+ * lambdas that capture by reference.
+ */
+
template <typename FunctionType>
-struct MakeFunction {};
+class FunctionRef;
template <typename ReturnType, typename... Args>
-struct MakeFunction<ReturnType(Args...)> {
- using type = Function<ReturnType(Args...), false>;
-};
+class FunctionRef<ReturnType(Args...)> final {
+ using Call = ReturnType (*)(void*, Args&&...);
-template <typename ReturnType, typename... Args>
-struct MakeFunction<ReturnType(Args...) const> {
- using type = Function<ReturnType(Args...), true>;
-};
-} // namespace impl
+ void* object_{nullptr};
+ Call call_{&FunctionRef::uninitCall};
-/* using override */ using impl::constCastFunction;
+ static ReturnType uninitCall(void*, Args&&...) {
+ throw std::bad_function_call();
+ }
-template <typename FunctionType>
-using Function = typename impl::MakeFunction<FunctionType>::type;
-}
+ template <typename Fun>
+ static ReturnType call(void* object, Args&&... args) {
+ return static_cast<ReturnType>(detail::function::invoke(
+ *static_cast<Fun*>(object), static_cast<Args&&>(args)...));
+ }
+
+ public:
+ /**
+ * Default constructor. Constructs an empty FunctionRef.
+ *
+ * Invoking it will throw std::bad_function_call.
+ */
+ FunctionRef() = default;
+
+ /**
+ * Construct a FunctionRef from a reference to a callable object.
+ */
+ template <typename Fun>
+ /* implicit */ FunctionRef(Fun&& fun) noexcept {
+ using ReferencedType = typename std::remove_reference<Fun>::type;
+
+ static_assert(
+ std::is_convertible<
+ typename std::result_of<ReferencedType&(Args && ...)>::type,
+ ReturnType>::value,
+ "FunctionRef cannot be constructed from object with "
+ "incompatible function signature");
+
+ // `Fun` may be a const type, in which case we have to do a const_cast
+ // to store the address in a `void*`. This is safe because the `void*`
+ // will be cast back to `Fun*` (which is a const pointer whenever `Fun`
+ // is a const type) inside `FunctionRef::call`
+ object_ = const_cast<void*>(static_cast<void const*>(std::addressof(fun)));
+ call_ = &FunctionRef::call<ReferencedType>;
+ }
+
+ ReturnType operator()(Args... args) const {
+ return call_(object_, static_cast<Args&&>(args)...);
+ }
+};
+
+} // namespace folly
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