| /* |
| * 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. |
| * 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> |
| |
| namespace folly { |
| |
| template <typename FunctionType> |
| class Function; |
| |
| template <typename ReturnType, typename... Args> |
| Function<ReturnType(Args...) const> constCastFunction( |
| Function<ReturnType(Args...)>&&) noexcept; |
| |
| namespace detail { |
| namespace function { |
| |
| enum class Op { MOVE, NUKE, FULL, HEAP }; |
| |
| union Data { |
| void* big; |
| std::aligned_storage<6 * sizeof(void*)>::type tiny; |
| }; |
| |
| template <typename Fun, typename FunT = typename std::decay<Fun>::type> |
| 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> |
| bool isNullPtrFn(T* p) { |
| return p == nullptr; |
| } |
| template <typename T> |
| std::false_type isNullPtrFn(T&&) { |
| return {}; |
| } |
| |
| 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)...); |
| } |
| |
| 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)...); |
| } |
| }; |
| }; |
| |
| 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)...); |
| } |
| |
| 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)...); |
| } |
| }; |
| }; |
| |
| 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 constexpr 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 constexpr 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 |
| |
| 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_{&detail::function::uninitNoop}; |
| |
| 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 { |
| that.exec_(Op::MOVE, &that.data_, &data_); |
| std::swap(call_, that.call_); |
| std::swap(exec_, that.exec_); |
| } |
| |
| public: |
| /** |
| * Default constructor. Constructs an empty Function. |
| */ |
| Function() = default; |
| |
| // not copyable |
| Function(const Function&) = delete; |
| |
| /** |
| * Move constructor |
| */ |
| 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 {} |
| |
| /** |
| * 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 < |
| 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 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; |
| |
| /** |
| * 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 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; |
| } |
| |
| /** |
| * Assigns a callable object to this `Function`. If the operation fails, |
| * `*this` is left unmodified. |
| * |
| * \note `typename = ResultOf<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(static_cast<Fun&&>(fun)); |
| } else { |
| // Construct a temporary and (nothrow) swap. |
| Function(static_cast<Fun&&>(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_(Op::FULL, nullptr, 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); |
| } |
| |
| namespace detail { |
| namespace function { |
| template <typename Fun, typename FunctionType, typename = void> |
| struct IsCallableAsImpl : std::false_type {}; |
| |
| template <typename Fun, typename ReturnType, typename... Args> |
| struct IsCallableAsImpl< |
| Fun, |
| ReturnType(Args...), |
| void_t<typename std::result_of<Fun && (Args && ...)>::type>> |
| : std::is_convertible< |
| typename std::result_of<Fun && (Args && ...)>::type, |
| ReturnType> {}; |
| |
| template <typename Fun, typename FunctionType> |
| struct IsCallableAs : IsCallableAsImpl<Fun, FunctionType> {}; |
| } |
| } |
| |
| /** |
| * @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>(detail::function::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>>>>, |
| detail::function::IsCallableAs<Fun, ReturnType(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 |