ecency-mobile/ios/Pods/Folly/folly/Function.h
2019-05-29 14:32:35 +03:00

951 lines
33 KiB
C++

/*
* 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