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- /*
- * Copyright 2016-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.
- * You may obtain a copy of the License at
- *
- * http://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.
- */
- /*
- * @author Eric Niebler (eniebler@fb.com), Sven Over (over@fb.com)
- * Acknowledgements: Giuseppe Ottaviano (ott@fb.com)
- */
- /**
- * @class Function
- *
- * @brief A polymorphic function wrapper that is not copyable and does not
- * require the wrapped function to be copy constructible.
- *
- * `folly::Function` is a polymorphic function wrapper, similar to
- * `std::function`. The template parameters of the `folly::Function` define
- * the parameter signature of the wrapped callable, but not the specific
- * type of the embedded callable. E.g. a `folly::Function<int(int)>`
- * can wrap callables that return an `int` when passed an `int`. This can be a
- * function pointer or any class object implementing one or both of
- *
- * int operator(int);
- * int operator(int) const;
- *
- * If both are defined, the non-const one takes precedence.
- *
- * Unlike `std::function`, a `folly::Function` can wrap objects that are not
- * copy constructible. As a consequence of this, `folly::Function` itself
- * is not copyable, either.
- *
- * Another difference is that, unlike `std::function`, `folly::Function` treats
- * const-ness of methods correctly. While a `std::function` allows to wrap
- * an object that only implements a non-const `operator()` and invoke
- * a const-reference of the `std::function`, `folly::Function` requires you to
- * declare a function type as const in order to be able to execute it on a
- * const-reference.
- *
- * For example:
- *
- * class Foo {
- * public:
- * void operator()() {
- * // mutates the Foo object
- * }
- * };
- *
- * class Bar {
- * std::function<void(void)> foo_; // wraps a Foo object
- * public:
- * void mutateFoo() const
- * {
- * foo_();
- * }
- * };
- *
- * Even though `mutateFoo` is a const-method, so it can only reference `foo_`
- * as const, it is able to call the non-const `operator()` of the Foo
- * object that is embedded in the foo_ function.
- *
- * `folly::Function` will not allow you to do that. You will have to decide
- * whether you need to invoke your wrapped callable from a const reference
- * (like in the example above), in which case it will only wrap a
- * `operator() const`. If your functor does not implement that,
- * compilation will fail. If you do not require to be able to invoke the
- * wrapped function in a const context, you can wrap any functor that
- * implements either or both of const and non-const `operator()`.
- *
- * The template parameter of `folly::Function`, the `FunctionType`, can be
- * const-qualified. Be aware that the const is part of the function signature.
- * It does not mean that the function type is a const type.
- *
- * using FunctionType = R(Args...);
- * using ConstFunctionType = R(Args...) const;
- *
- * In this example, `FunctionType` and `ConstFunctionType` are different
- * types. `ConstFunctionType` is not the same as `const FunctionType`.
- * As a matter of fact, trying to use the latter should emit a compiler
- * warning or error, because it has no defined meaning.
- *
- * // This will not compile:
- * folly::Function<void(void) const> func = Foo();
- * // because Foo does not have a member function of the form:
- * // void operator()() const;
- *
- * // This will compile just fine:
- * folly::Function<void(void)> func = Foo();
- * // and it will wrap the existing member function:
- * // void operator()();
- *
- * When should a const function type be used? As a matter of fact, you will
- * probably not need to use const function types very often. See the following
- * example:
- *
- * class Bar {
- * folly::Function<void()> func_;
- * folly::Function<void() const> constFunc_;
- *
- * void someMethod() {
- * // Can call func_.
- * func_();
- * // Can call constFunc_.
- * constFunc_();
- * }
- *
- * void someConstMethod() const {
- * // Can call constFunc_.
- * constFunc_();
- * // However, cannot call func_ because a non-const method cannot
- * // be called from a const one.
- * }
- * };
- *
- * As you can see, whether the `folly::Function`'s function type should
- * be declared const or not is identical to whether a corresponding method
- * would be declared const or not.
- *
- * You only require a `folly::Function` to hold a const function type, if you
- * intend to invoke it from within a const context. This is to ensure that
- * you cannot mutate its inner state when calling in a const context.
- *
- * This is how the const/non-const choice relates to lambda functions:
- *
- * // Non-mutable lambdas: can be stored in a non-const...
- * folly::Function<void(int)> print_number =
- * [] (int number) { std::cout << number << std::endl; };
- *
- * // ...as well as in a const folly::Function
- * folly::Function<void(int) const> print_number_const =
- * [] (int number) { std::cout << number << std::endl; };
- *
- * // Mutable lambda: can only be stored in a non-const folly::Function:
- * int number = 0;
- * folly::Function<void()> print_number =
- * [number] () mutable { std::cout << ++number << std::endl; };
- * // Trying to store the above mutable lambda in a
- * // `folly::Function<void() const>` would lead to a compiler error:
- * // error: no viable conversion from '(lambda at ...)' to
- * // 'folly::Function<void () const>'
- *
- * Casting between const and non-const `folly::Function`s:
- * conversion from const to non-const signatures happens implicitly. Any
- * function that takes a `folly::Function<R(Args...)>` can be passed
- * a `folly::Function<R(Args...) const>` without explicit conversion.
- * This is safe, because casting from const to non-const only entails giving
- * up the ability to invoke the function from a const context.
- * Casting from a non-const to a const signature is potentially dangerous,
- * as it means that a function that may change its inner state when invoked
- * is made possible to call from a const context. Therefore this cast does
- * not happen implicitly. The function `folly::constCastFunction` can
- * be used to perform the cast.
- *
- * // Mutable lambda: can only be stored in a non-const folly::Function:
- * int number = 0;
- * folly::Function<void()> print_number =
- * [number] () mutable { std::cout << ++number << std::endl; };
- *
- * // const-cast to a const folly::Function:
- * folly::Function<void() const> print_number_const =
- * constCastFunction(std::move(print_number));
- *
- * When to use const function types?
- * Generally, only when you need them. When you use a `folly::Function` as a
- * member of a struct or class, only use a const function signature when you
- * need to invoke the function from const context.
- * When passing a `folly::Function` to a function, the function should accept
- * a non-const `folly::Function` whenever possible, i.e. when it does not
- * need to pass on or store a const `folly::Function`. This is the least
- * possible constraint: you can always pass a const `folly::Function` when
- * the function accepts a non-const one.
- *
- * How does the const behaviour compare to `std::function`?
- * `std::function` can wrap object with non-const invokation behaviour but
- * exposes them as const. The equivalent behaviour can be achieved with
- * `folly::Function` like so:
- *
- * std::function<void(void)> stdfunc = someCallable;
- *
- * folly::Function<void(void) const> uniqfunc = constCastFunction(
- * folly::Function<void(void)>(someCallable)
- * );
- *
- * You need to wrap the callable first in a non-const `folly::Function` to
- * select a non-const invoke operator (or the const one if no non-const one is
- * present), and then move it into a const `folly::Function` using
- * `constCastFunction`.
- * The name of `constCastFunction` should warn you that something
- * potentially dangerous is happening. As a matter of fact, using
- * `std::function` always involves this potentially dangerous aspect, which
- * is why it is not considered fully const-safe or even const-correct.
- * However, in most of the cases you will not need the dangerous aspect at all.
- * Either you do not require invokation of the function from a const context,
- * in which case you do not need to use `constCastFunction` and just
- * use the inner `folly::Function` in the example above, i.e. just use a
- * non-const `folly::Function`. Or, you may need invokation from const, but
- * the callable you are wrapping does not mutate its state (e.g. it is a class
- * object and implements `operator() const`, or it is a normal,
- * non-mutable lambda), in which case you can wrap the callable in a const
- * `folly::Function` directly, without using `constCastFunction`.
- * Only if you require invokation from a const context of a callable that
- * may mutate itself when invoked you have to go through the above procedure.
- * However, in that case what you do is potentially dangerous and requires
- * the equivalent of a `const_cast`, hence you need to call
- * `constCastFunction`.
- */
- #pragma once
- #include <functional>
- #include <memory>
- #include <new>
- #include <type_traits>
- #include <utility>
- #include <folly/CppAttributes.h>
- #include <folly/Portability.h>
- #include <folly/Traits.h>
- #include <folly/functional/Invoke.h>
- #include <folly/lang/Exception.h>
- namespace folly {
- template <typename FunctionType>
- class Function;
- template <typename ReturnType, typename... Args>
- Function<ReturnType(Args...) const> constCastFunction(
- Function<ReturnType(Args...)>&&) noexcept;
- #if FOLLY_HAVE_NOEXCEPT_FUNCTION_TYPE
- template <typename ReturnType, typename... Args>
- Function<ReturnType(Args...) const noexcept> constCastFunction(
- Function<ReturnType(Args...) noexcept>&&) noexcept;
- #endif
- namespace detail {
- namespace function {
- enum class Op { MOVE, NUKE, HEAP };
- union Data {
- Data() {}
- void* big;
- std::aligned_storage<6 * sizeof(void*)>::type tiny;
- };
- template <typename Fun, typename = Fun*>
- using IsSmall = Conjunction<
- bool_constant<(sizeof(Fun) <= sizeof(Data::tiny))>,
- std::is_nothrow_move_constructible<Fun>>;
- using SmallTag = std::true_type;
- using HeapTag = std::false_type;
- template <typename T>
- struct NotFunction : std::true_type {};
- template <typename T>
- struct NotFunction<Function<T>> : std::false_type {};
- template <typename T>
- using EnableIfNotFunction =
- typename std::enable_if<NotFunction<T>::value>::type;
- struct CoerceTag {};
- template <typename T>
- bool isNullPtrFn(T* p) {
- return p == nullptr;
- }
- template <typename T>
- std::false_type isNullPtrFn(T&&) {
- return {};
- }
- template <typename F, typename... Args>
- using CallableResult = decltype(std::declval<F>()(std::declval<Args>()...));
- template <
- typename From,
- typename To,
- typename = typename std::enable_if<
- !std::is_reference<To>::value || std::is_reference<From>::value>::type>
- using SafeResultOf = decltype(static_cast<To>(std::declval<From>()));
- 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>
- using ResultOf =
- SafeResultOf<CallableResult<_t<std::decay<F>>&, Args...>, ReturnType>;
- 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<NonConstSignature>*>(this);
- return fn.call_(fn.data_, static_cast<Args&&>(args)...);
- }
- class SharedProxy {
- std::shared_ptr<Function<NonConstSignature>> sp_;
- public:
- explicit SharedProxy(Function<NonConstSignature>&& func)
- : sp_(std::make_shared<Function<NonConstSignature>>(std::move(func))) {}
- 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>
- using ResultOf = SafeResultOf<
- CallableResult<const _t<std::decay<F>>&, Args...>,
- ReturnType>;
- 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<ConstSignature>*>(this);
- return fn.call_(fn.data_, static_cast<Args&&>(args)...);
- }
- class SharedProxy {
- std::shared_ptr<Function<ConstSignature>> sp_;
- public:
- explicit SharedProxy(Function<ConstSignature>&& func)
- : sp_(std::make_shared<Function<ConstSignature>>(std::move(func))) {}
- ReturnType operator()(Args&&... args) const {
- return (*sp_)(static_cast<Args&&>(args)...);
- }
- };
- };
- #if FOLLY_HAVE_NOEXCEPT_FUNCTION_TYPE
- template <typename ReturnType, typename... Args>
- struct FunctionTraits<ReturnType(Args...) noexcept> {
- using Call = ReturnType (*)(Data&, Args&&...) noexcept;
- using IsConst = std::false_type;
- using ConstSignature = ReturnType(Args...) const noexcept;
- using NonConstSignature = ReturnType(Args...) noexcept;
- using OtherSignature = ConstSignature;
- template <typename F>
- using ResultOf =
- SafeResultOf<CallableResult<_t<std::decay<F>>&, Args...>, ReturnType>;
- template <typename Fun>
- static ReturnType callSmall(Data& p, Args&&... args) noexcept {
- 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) noexcept {
- return static_cast<ReturnType>(
- (*static_cast<Fun*>(p.big))(static_cast<Args&&>(args)...));
- }
- static ReturnType uninitCall(Data&, Args&&...) noexcept {
- terminate_with<std::bad_function_call>();
- }
- ReturnType operator()(Args... args) noexcept {
- auto& fn = *static_cast<Function<NonConstSignature>*>(this);
- return fn.call_(fn.data_, static_cast<Args&&>(args)...);
- }
- class SharedProxy {
- std::shared_ptr<Function<NonConstSignature>> sp_;
- public:
- explicit SharedProxy(Function<NonConstSignature>&& func)
- : sp_(std::make_shared<Function<NonConstSignature>>(std::move(func))) {}
- ReturnType operator()(Args&&... args) const {
- return (*sp_)(static_cast<Args&&>(args)...);
- }
- };
- };
- template <typename ReturnType, typename... Args>
- struct FunctionTraits<ReturnType(Args...) const noexcept> {
- using Call = ReturnType (*)(Data&, Args&&...) noexcept;
- using IsConst = std::true_type;
- using ConstSignature = ReturnType(Args...) const noexcept;
- using NonConstSignature = ReturnType(Args...) noexcept;
- using OtherSignature = NonConstSignature;
- template <typename F>
- using ResultOf = SafeResultOf<
- CallableResult<const _t<std::decay<F>>&, Args...>,
- ReturnType>;
- template <typename Fun>
- static ReturnType callSmall(Data& p, Args&&... args) noexcept {
- 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) noexcept {
- return static_cast<ReturnType>(
- (*static_cast<const Fun*>(p.big))(static_cast<Args&&>(args)...));
- }
- static ReturnType uninitCall(Data&, Args&&...) noexcept {
- throw std::bad_function_call();
- }
- ReturnType operator()(Args... args) const noexcept {
- auto& fn = *static_cast<const Function<ConstSignature>*>(this);
- return fn.call_(fn.data_, static_cast<Args&&>(args)...);
- }
- class SharedProxy {
- std::shared_ptr<Function<ConstSignature>> sp_;
- public:
- explicit SharedProxy(Function<ConstSignature>&& func)
- : sp_(std::make_shared<Function<ConstSignature>>(std::move(func))) {}
- ReturnType operator()(Args&&... args) const {
- return (*sp_)(static_cast<Args&&>(args)...);
- }
- };
- };
- #endif
- 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::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::HEAP:
- break;
- }
- return true;
- }
- } // namespace function
- } // namespace detail
- 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 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 Fun>
- using IsSmall = detail::function::IsSmall<Fun>;
- // 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_{nullptr};
- bool exec(Op o, Data* src, Data* dst) const {
- return exec_ && exec_(o, src, dst);
- }
- friend Traits;
- friend Function<typename Traits::ConstSignature> folly::constCastFunction<>(
- Function<typename Traits::NonConstSignature>&&) noexcept;
- friend class Function<typename Traits::OtherSignature>;
- template <typename Fun>
- Function(Fun&& fun, SmallTag) noexcept {
- using FunT = typename std::decay<Fun>::type;
- if (!detail::function::isNullPtrFn(fun)) {
- ::new (static_cast<void*>(&data_.tiny)) FunT(static_cast<Fun&&>(fun));
- call_ = &Traits::template callSmall<FunT>;
- exec_ = &detail::function::execSmall<FunT>;
- }
- }
- template <typename Fun>
- Function(Fun&& fun, HeapTag) {
- using FunT = typename std::decay<Fun>::type;
- data_.big = new FunT(static_cast<Fun&&>(fun));
- call_ = &Traits::template callBig<FunT>;
- exec_ = &detail::function::execBig<FunT>;
- }
- template <typename Signature>
- Function(Function<Signature>&& that, CoerceTag)
- : Function(static_cast<Function<Signature>&&>(that), HeapTag{}) {}
- Function(Function<typename Traits::OtherSignature>&& that, CoerceTag) noexcept
- : call_(that.call_), exec_(that.exec_) {
- that.call_ = &Traits::uninitCall;
- that.exec_ = nullptr;
- exec(Op::MOVE, &that.data_, &data_);
- }
- public:
- /**
- * Default constructor. Constructs an empty Function.
- */
- Function() = default;
- // not copyable
- Function(const Function&) = delete;
- #if __OBJC__
- // Make sure Objective C blocks are copied
- template <class ReturnType, class... Args>
- /*implicit*/ Function(ReturnType (^objCBlock)(Args... args))
- : Function([blockCopy = (ReturnType(^)(Args...))[objCBlock copy]](
- Args... args) { return blockCopy(args...); }){};
- #endif
- /**
- * Move constructor
- */
- Function(Function&& that) noexcept : call_(that.call_), exec_(that.exec_) {
- // that must be uninitialized before exec() call in the case of self move
- that.call_ = &Traits::uninitCall;
- that.exec_ = nullptr;
- exec(Op::MOVE, &that.data_, &data_);
- }
- /**
- * Constructs an empty `Function`.
- */
- /* implicit */ Function(std::nullptr_t) noexcept {}
- /**
- * 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 Traits::template 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 <
- typename Fun,
- typename = detail::function::EnableIfNotFunction<Fun>,
- typename = typename Traits::template ResultOf<Fun>>
- /* implicit */ Function(Fun fun) noexcept(
- IsSmall<Fun>::value&& noexcept(Fun(std::declval<Fun>())))
- : Function(std::move(fun), IsSmall<Fun>{}) {}
- /**
- * 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 <
- 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{}) {}
- /**
- * If `ptr` is null, constructs an empty `Function`. Otherwise,
- * this constructor is equivalent to `Function(std::mem_fn(ptr))`.
- */
- template <
- typename Member,
- typename Class,
- // 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 {
- if (ptr) {
- *this = std::mem_fn(ptr);
- }
- }
- ~Function() {
- exec(Op::NUKE, &data_, nullptr);
- }
- Function& operator=(const Function&) = delete;
- #if __OBJC__
- // Make sure Objective C blocks are copied
- template <class ReturnType, class... Args>
- /* implicit */ Function& operator=(ReturnType (^objCBlock)(Args... args)) {
- (*this) = [blockCopy = (ReturnType(^)(Args...))[objCBlock copy]](
- Args... args) { return blockCopy(args...); };
- return *this;
- }
- #endif
- /**
- * 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 {
- // Q: Why is it 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;
- }
- /**
- * Assigns a callable object to this `Function`. If the operation fails,
- * `*this` is left unmodified.
- *
- * \note `typename = decltype(Function(std::declval<Fun>()))` prevents this
- * overload from being selected by overload resolution when `fun` is not a
- * compatible function.
- */
- 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.
- if (noexcept(/* implicit */ Function(std::declval<Fun>()))) {
- // Q: Why is is safe to destroy and reconstruct this object in place?
- // A: See the explanation in the move assignment operator.
- this->~Function();
- ::new (this) Function(std::move(fun));
- } else {
- // Construct a temporary and (nothrow) swap.
- Function(std::move(fun)).swap(*this);
- }
- 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`.
- */
- Function& operator=(std::nullptr_t) noexcept {
- return (*this = Function());
- }
- /**
- * If `ptr` is null, clears this `Function`. Otherwise, this assignment
- * operator is equivalent to `*this = std::mem_fn(ptr)`.
- */
- template <typename Member, typename Class>
- auto operator=(Member Class::*ptr) noexcept
- // Prevent this overload from being selected when `ptr` is not a
- // compatible member function pointer.
- -> decltype(operator=(std::mem_fn(ptr))) {
- return ptr ? (*this = std::mem_fn(ptr)) : (*this = Function());
- }
- /**
- * Call the wrapped callable object with the specified arguments.
- */
- using Traits::operator();
- /**
- * Exchanges the callable objects of `*this` and `that`.
- */
- void swap(Function& that) noexcept {
- std::swap(*this, that);
- }
- /**
- * Returns `true` if this `Function` contains a callable, i.e. is
- * non-empty.
- */
- explicit operator bool() const noexcept {
- return exec_ != nullptr;
- }
- /**
- * Returns `true` if this `Function` stores the callable on the
- * heap. If `false` is returned, there has been no additional memory
- * allocation and the callable is stored inside the `Function`
- * object itself.
- */
- bool hasAllocatedMemory() const noexcept {
- 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() && {
- return std::move(*this).asSharedProxy();
- }
- };
- template <typename FunctionType>
- void swap(Function<FunctionType>& lhs, Function<FunctionType>& rhs) noexcept {
- lhs.swap(rhs);
- }
- template <typename FunctionType>
- bool operator==(const Function<FunctionType>& fn, std::nullptr_t) {
- return !fn;
- }
- template <typename FunctionType>
- bool operator==(std::nullptr_t, const Function<FunctionType>& fn) {
- return !fn;
- }
- template <typename FunctionType>
- bool operator!=(const Function<FunctionType>& fn, std::nullptr_t) {
- return !(fn == nullptr);
- }
- 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...) const> constCastFunction(
- Function<ReturnType(Args...)>&& that) noexcept {
- return Function<ReturnType(Args...) const>{std::move(that),
- detail::function::CoerceTag{}};
- }
- template <typename ReturnType, typename... Args>
- Function<ReturnType(Args...) const> constCastFunction(
- Function<ReturnType(Args...) const>&& that) noexcept {
- return std::move(that);
- }
- #if FOLLY_HAVE_NOEXCEPT_FUNCTION_TYPE
- template <typename ReturnType, typename... Args>
- Function<ReturnType(Args...) const noexcept> constCastFunction(
- Function<ReturnType(Args...) noexcept>&& that) noexcept {
- return Function<ReturnType(Args...) const noexcept>{
- std::move(that), detail::function::CoerceTag{}};
- }
- template <typename ReturnType, typename... Args>
- Function<ReturnType(Args...) const noexcept> constCastFunction(
- Function<ReturnType(Args...) const noexcept>&& that) noexcept {
- return std::move(that);
- }
- #endif
- /**
- * @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&&...);
- static ReturnType uninitCall(void*, Args&&...) {
- throw std::bad_function_call();
- }
- template <typename Fun>
- static ReturnType call(void* object, Args&&... args) {
- using Pointer = _t<std::add_pointer<Fun>>;
- return static_cast<ReturnType>(invoke(
- static_cast<Fun&&>(*static_cast<Pointer>(object)),
- static_cast<Args&&>(args)...));
- }
- void* object_{nullptr};
- Call call_{&FunctionRef::uninitCall};
- 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<
- Conjunction<
- Negation<std::is_same<FunctionRef, _t<std::decay<Fun>>>>,
- is_invocable_r<ReturnType, Fun&&, Args&&...>>::value,
- int>::type = 0>
- constexpr /* implicit */ FunctionRef(Fun&& fun) noexcept
- // `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<Fun>) {}
- ReturnType operator()(Args... args) const {
- return call_(object_, static_cast<Args&&>(args)...);
- }
- constexpr explicit operator bool() const {
- return object_;
- }
- };
- } // namespace folly
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