/*
- * Copyright 2016 Facebook, Inc.
- *
- * @author Eric Niebler (eniebler@fb.com), Sven Over (over@fb.com)
+ * Copyright 2017-present Facebook, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* 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.
- *
+ */
+/*
+ * @author Eric Niebler (eniebler@fb.com), Sven Over (over@fb.com)
* Acknowledgements: Giuseppe Ottaviano (ott@fb.com)
*/
#include <folly/CppAttributes.h>
#include <folly/Portability.h>
+#include <folly/Traits.h>
namespace folly {
};
template <typename Fun, typename FunT = typename std::decay<Fun>::type>
-using IsSmall = std::integral_constant<
- bool,
- (sizeof(FunT) <= sizeof(Data::tiny) &&
- // Same as is_nothrow_move_constructible, but w/ no template instantiation.
- noexcept(FunT(std::declval<FunT&&>()))
- )>;
+using IsSmall = Conjunction<
+ std::integral_constant<bool, (sizeof(FunT) <= sizeof(Data::tiny))>,
+ std::is_nothrow_move_constructible<FunT>>;
using SmallTag = std::true_type;
using HeapTag = std::false_type;
+template <class T>
+struct NotFunction : std::true_type {};
+template <class T>
+struct NotFunction<Function<T>> : std::false_type {};
+
+template <typename Fun, typename FunT = typename std::decay<Fun>::type>
+using DecayIfConstructible = typename std::enable_if<
+ Conjunction<NotFunction<FunT>, std::is_constructible<FunT, Fun>>::value,
+ FunT>::type;
+
struct CoerceTag {};
template <typename T>
return fn.call_(fn.data_, static_cast<Args&&>(args)...);
}
- struct SharedFunctionImpl {
+ class SharedProxy {
std::shared_ptr<Function<ReturnType(Args...)>> sp_;
+
+ public:
+ explicit SharedProxy(Function<ReturnType(Args...)>&& func)
+ : sp_(std::make_shared<Function<ReturnType(Args...)>>(
+ std::move(func))) {}
ReturnType operator()(Args&&... args) const {
return (*sp_)(static_cast<Args&&>(args)...);
}
return fn.call_(fn.data_, static_cast<Args&&>(args)...);
}
- struct SharedFunctionImpl {
+ class SharedProxy {
std::shared_ptr<Function<ReturnType(Args...) const>> sp_;
+
+ public:
+ explicit SharedProxy(Function<ReturnType(Args...) const>&& func)
+ : sp_(std::make_shared<Function<ReturnType(Args...) const>>(
+ std::move(func))) {}
ReturnType operator()(Args&&... args) const {
return (*sp_)(static_cast<Args&&>(args)...);
}
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
-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
template <typename Fun>
using IsSmall = detail::function::IsSmall<Fun>;
- 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`
friend Traits;
friend Function<typename Traits::ConstSignature> folly::constCastFunction<>(
Function<typename Traits::NonConstSignature>&&) noexcept;
- friend class Function<OtherSignature>;
+ friend class Function<typename Traits::OtherSignature>;
template <typename Fun>
Function(Fun&& fun, SmallTag) noexcept {
exec_ = &detail::function::execBig<FunT>;
}
- Function(Function<OtherSignature>&& that, CoerceTag) noexcept {
+ template <typename Signature>
+ Function(Function<Signature>&& that, CoerceTag)
+ : Function(static_cast<Function<Signature>&&>(that), HeapTag{}) {}
+
+ Function(
+ Function<typename Traits::OtherSignature>&& that,
+ CoerceTag) noexcept {
that.exec_(Op::MOVE, &that.data_, &data_);
std::swap(call_, that.call_);
std::swap(exec_, that.exec_);
Function() = default;
// not copyable
- // NOTE: Deleting the non-const copy constructor is unusual but necessary to
- // prevent copies from non-const `Function` object from selecting the
- // perfect forwarding implicit converting constructor below
- // (i.e., `template <typename Fun> Function(Fun&&)`).
- Function(Function&) = delete;
Function(const Function&) = delete;
/**
/* implicit */ Function(std::nullptr_t) noexcept {}
/**
- * Constructs a new `Function` from any callable object. This
- * handles function pointers, pointers to static member functions,
- * `std::reference_wrapper` objects, `std::function` objects, and arbitrary
- * objects that implement `operator()` if the parameter signature
- * matches (i.e. it returns R when called with Args...).
- * For a `Function` with a const function type, the object must be
- * callable from a const-reference, i.e. implement `operator() const`.
- * For a `Function` with a non-const function type, the object will
- * be called from a non-const reference, which means that it will execute
- * a non-const `operator()` if it is defined, and falls back to
- * `operator() const` otherwise.
+ * Constructs a new `Function` from any callable object that is _not_ a
+ * `folly::Function`. This handles function pointers, pointers to static
+ * member functions, `std::reference_wrapper` objects, `std::function`
+ * objects, and arbitrary objects that implement `operator()` if the parameter
+ * signature matches (i.e. it returns an object convertible to `R` when called
+ * with `Args...`).
*
* \note `typename = ResultOf<Fun>` prevents this overload from being
* selected by overload resolution when `fun` is not a compatible function.
+ *
+ * \note The noexcept requires some explanation. IsSmall is true when the
+ * decayed type fits within the internal buffer and is noexcept-movable. But
+ * this ctor might copy, not move. What we need here, if this ctor does a
+ * copy, is that this ctor be noexcept when the copy is noexcept. That is not
+ * checked in IsSmall, and shouldn't be, because once the Function is
+ * constructed, the contained object is never copied. This check is for this
+ * ctor only, in the case that this ctor does a copy.
*/
- template <class Fun, typename = typename Traits::template ResultOf<Fun>>
- /* implicit */ Function(Fun&& fun) noexcept(IsSmall<Fun>::value)
+ template <
+ typename Fun,
+ typename FunT = detail::function::DecayIfConstructible<Fun>,
+ typename = typename Traits::template ResultOf<Fun>>
+ /* implicit */ Function(Fun&& fun) noexcept(
+ IsSmall<Fun>::value && noexcept(FunT(std::declval<Fun>())))
: Function(static_cast<Fun&&>(fun), IsSmall<Fun>{}) {}
/**
- * For moving a `Function<X(Ys..) const>` into a `Function<X(Ys...)>`.
+ * For move-constructing from a `folly::Function<X(Ys...) [const?]>`.
+ * For a `Function` with a `const` function type, the object must be
+ * callable from a `const`-reference, i.e. implement `operator() const`.
+ * For a `Function` with a non-`const` function type, the object will
+ * be called from a non-const reference, which means that it will execute
+ * a non-const `operator()` if it is defined, and falls back to
+ * `operator() const` otherwise.
*/
template <
- bool Const = Traits::IsConst::value,
- typename std::enable_if<!Const, int>::type = 0>
- Function(Function<OtherSignature>&& that) noexcept
+ typename Signature,
+ typename = typename Traits::template ResultOf<Function<Signature>>>
+ Function(Function<Signature>&& that) noexcept(
+ noexcept(Function(std::move(that), CoerceTag{})))
: Function(std::move(that), CoerceTag{}) {}
/**
exec_(Op::NUKE, &data_, nullptr);
}
- Function& operator=(Function&) = delete;
Function& operator=(const Function&) = delete;
/**
* Move assignment operator
+ *
+ * \note Leaves `that` in a valid but unspecified state. If `&that == this`
+ * then `*this` is left in a valid but unspecified state.
*/
Function& operator=(Function&& that) noexcept {
- if (&that != this) {
- // Q: Why is is safe to destroy and reconstruct this object in place?
- // A: Two reasons: First, `Function` is a final class, so in doing this
- // we aren't slicing off any derived parts. And second, the move
- // operation is guaranteed not to throw so we always leave the object
- // in a valid state.
- this->~Function();
- ::new (this) Function(std::move(that));
- }
+ // Q: Why is is safe to destroy and reconstruct this object in place?
+ // A: Two reasons: First, `Function` is a final class, so in doing this
+ // we aren't slicing off any derived parts. And second, the move
+ // operation is guaranteed not to throw so we always leave the object
+ // in a valid state.
+ // In the case of self-move (this == &that), this leaves the object in
+ // a default-constructed state. First the object is destroyed, then we
+ // pass the destroyed object to the move constructor. The first thing the
+ // move constructor does is default-construct the object. That object is
+ // "moved" into itself, which is a no-op for a default-constructed Function.
+ this->~Function();
+ ::new (this) Function(std::move(that));
return *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 = typename Traits::template ResultOf<Fun>>
+ template <typename Fun, typename = decltype(Function(std::declval<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.
return *this;
}
+ /**
+ * For assigning from a `Function<X(Ys..) [const?]>`.
+ */
+ template <
+ typename Signature,
+ typename = typename Traits::template ResultOf<Function<Signature>>>
+ Function& operator=(Function<Signature>&& that) noexcept(
+ noexcept(Function(std::move(that)))) {
+ return (*this = Function(std::move(that)));
+ }
+
/**
* Clears this `Function`.
*/
return exec_(Op::HEAP, nullptr, nullptr);
}
+ using typename Traits::SharedProxy;
+
+ /**
+ * Move this `Function` into a copyable callable object, of which all copies
+ * share the state.
+ */
+ SharedProxy asSharedProxy() && {
+ return SharedProxy{std::move(*this)};
+ }
+
/**
* Construct a `std::function` by moving in the contents of this `Function`.
* 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<typename Traits::NonConstSignature> asStdFunction() && {
- using Impl = typename Traits::SharedFunctionImpl;
- return Impl{std::make_shared<Function>(std::move(*this))};
+ return std::move(*this).asSharedProxy();
}
};
-FOLLY_POP_WARNING
template <typename FunctionType>
void swap(Function<FunctionType>& lhs, Function<FunctionType>& rhs) noexcept {
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>
+class FunctionRef;
+
+template <typename ReturnType, typename... Args>
+class FunctionRef<ReturnType(Args...)> final {
+ using Call = ReturnType (*)(void*, Args&&...);
+
+ void* object_{nullptr};
+ Call call_{&FunctionRef::uninitCall};
+
+ static ReturnType uninitCall(void*, Args&&...) {
+ throw std::bad_function_call();
+ }
+
+ 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,
+ typename std::enable_if<
+ !std::is_same<FunctionRef, typename std::decay<Fun>::type>::value,
+ int>::type = 0>
+ /* 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)...);
+ }
+
+ explicit operator bool() const {
+ return object_;
+ }
+};
+
} // namespace folly
projects / folly.git / blobdiff