1160 lines
40 KiB
C++
1160 lines
40 KiB
C++
/*
|
|
* Copyright (c) Meta Platforms, Inc. and affiliates.
|
|
*
|
|
* 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.
|
|
*/
|
|
|
|
//
|
|
// Docs: https://fburl.com/fbcref_function
|
|
//
|
|
|
|
/**
|
|
* @class folly::Function
|
|
* @refcode folly/docs/examples/folly/Function.cpp
|
|
*
|
|
* 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 invocation 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`.
|
|
*/
|
|
|
|
#pragma once
|
|
|
|
#include <cstring>
|
|
#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/Align.h>
|
|
#include <folly/lang/Exception.h>
|
|
#include <folly/lang/New.h>
|
|
|
|
namespace folly {
|
|
|
|
template <typename FunctionType>
|
|
class Function;
|
|
|
|
template <typename ReturnType, typename... Args>
|
|
Function<ReturnType(Args...) const> constCastFunction(
|
|
Function<ReturnType(Args...)>&&) noexcept;
|
|
|
|
template <typename ReturnType, typename... Args>
|
|
Function<ReturnType(Args...) const noexcept> constCastFunction(
|
|
Function<ReturnType(Args...) noexcept>&&) noexcept;
|
|
|
|
namespace detail {
|
|
namespace function {
|
|
|
|
enum class Op { MOVE, NUKE, HEAP };
|
|
|
|
union Data {
|
|
struct BigTrivialLayout {
|
|
void* big;
|
|
std::size_t size;
|
|
std::size_t align;
|
|
};
|
|
|
|
void* big;
|
|
BigTrivialLayout bigt;
|
|
std::aligned_storage<6 * sizeof(void*)>::type tiny;
|
|
};
|
|
|
|
struct CoerceTag {};
|
|
|
|
template <typename T>
|
|
using FunctionNullptrTest =
|
|
decltype(static_cast<bool>(static_cast<T const&>(T(nullptr)) == nullptr));
|
|
|
|
template <typename T>
|
|
constexpr bool IsNullptrCompatible = is_detected_v<FunctionNullptrTest, T>;
|
|
|
|
template <typename T, std::enable_if_t<!IsNullptrCompatible<T>, int> = 0>
|
|
constexpr bool isEmptyFunction(T const&) {
|
|
return false;
|
|
}
|
|
template <typename T, std::enable_if_t<IsNullptrCompatible<T>, int> = 0>
|
|
constexpr bool isEmptyFunction(T const& t) {
|
|
return static_cast<bool>(t == nullptr);
|
|
}
|
|
|
|
template <typename F, typename... Args>
|
|
using CallableResult = decltype(FOLLY_DECLVAL(F&&)(FOLLY_DECLVAL(Args&&)...));
|
|
|
|
template <typename F, typename... Args>
|
|
constexpr bool CallableNoexcept =
|
|
noexcept(FOLLY_DECLVAL(F&&)(FOLLY_DECLVAL(Args&&)...));
|
|
|
|
template <
|
|
typename From,
|
|
typename To,
|
|
typename = typename std::enable_if<
|
|
!std::is_reference<To>::value || std::is_reference<From>::value>::type>
|
|
using IfSafeResultImpl = decltype(void(static_cast<To>(FOLLY_DECLVAL(From))));
|
|
|
|
#if defined(_MSC_VER)
|
|
// Need a workaround for MSVC to avoid the inscrutable error:
|
|
//
|
|
// folly\function.h(...) : fatal error C1001: An internal error has
|
|
// occurred in the compiler.
|
|
// (compiler file 'f:\dd\vctools\compiler\utc\src\p2\main.c', line 258)
|
|
// To work around this problem, try simplifying or changing the program
|
|
// near the locations listed above.
|
|
template <typename T>
|
|
using CallArg = T&&;
|
|
#else
|
|
template <typename T>
|
|
using CallArg = conditional_t<is_register_pass_v<T>, T, T&&>;
|
|
#endif
|
|
|
|
template <typename F, bool Nx, typename R, typename... A>
|
|
class FunctionTraitsSharedProxy {
|
|
std::shared_ptr<Function<F>> sp_;
|
|
|
|
public:
|
|
explicit FunctionTraitsSharedProxy(std::nullptr_t) noexcept {}
|
|
explicit FunctionTraitsSharedProxy(Function<F>&& func)
|
|
: sp_(func ? std::make_shared<Function<F>>(std::move(func))
|
|
: std::shared_ptr<Function<F>>()) {}
|
|
R operator()(A... args) const noexcept(Nx) {
|
|
if (!sp_) {
|
|
throw_exception<std::bad_function_call>();
|
|
}
|
|
return (*sp_)(static_cast<A&&>(args)...);
|
|
}
|
|
|
|
explicit operator bool() const noexcept { return sp_ != nullptr; }
|
|
|
|
friend bool operator==(
|
|
FunctionTraitsSharedProxy const& proxy, std::nullptr_t) noexcept {
|
|
return proxy.sp_ == nullptr;
|
|
}
|
|
friend bool operator!=(
|
|
FunctionTraitsSharedProxy const& proxy, std::nullptr_t) noexcept {
|
|
return proxy.sp_ != nullptr;
|
|
}
|
|
|
|
friend bool operator==(
|
|
std::nullptr_t, FunctionTraitsSharedProxy const& proxy) noexcept {
|
|
return proxy.sp_ == nullptr;
|
|
}
|
|
friend bool operator!=(
|
|
std::nullptr_t, FunctionTraitsSharedProxy const& proxy) noexcept {
|
|
return proxy.sp_ != nullptr;
|
|
}
|
|
};
|
|
|
|
template <
|
|
typename Fun,
|
|
bool Small,
|
|
bool Nx,
|
|
typename ReturnType,
|
|
typename... Args>
|
|
ReturnType call_(Args... args, Data& p) noexcept(Nx) {
|
|
auto& fn = *static_cast<Fun*>(Small ? &p.tiny : p.big);
|
|
if constexpr (std::is_void<ReturnType>::value) {
|
|
fn(static_cast<Args&&>(args)...);
|
|
} else {
|
|
return fn(static_cast<Args&&>(args)...);
|
|
}
|
|
}
|
|
|
|
template <typename FunctionType>
|
|
struct FunctionTraits;
|
|
|
|
template <typename ReturnType, typename... Args>
|
|
struct FunctionTraits<ReturnType(Args...)> {
|
|
using Call = ReturnType (*)(CallArg<Args>..., Data&);
|
|
using ConstSignature = ReturnType(Args...) const;
|
|
using NonConstSignature = ReturnType(Args...);
|
|
using OtherSignature = ConstSignature;
|
|
|
|
template <typename F, typename R = CallableResult<F&, Args...>>
|
|
using IfSafeResult = IfSafeResultImpl<R, ReturnType>;
|
|
|
|
template <typename Fun, bool Small>
|
|
static constexpr Call call =
|
|
call_<Fun, Small, false, ReturnType, CallArg<Args>...>;
|
|
|
|
static ReturnType uninitCall(CallArg<Args>..., Data&) {
|
|
throw_exception<std::bad_function_call>();
|
|
}
|
|
|
|
ReturnType operator()(Args... args) {
|
|
auto& fn = *static_cast<Function<NonConstSignature>*>(this);
|
|
return fn.call_(static_cast<Args&&>(args)..., fn.data_);
|
|
}
|
|
|
|
using SharedProxy =
|
|
FunctionTraitsSharedProxy<NonConstSignature, false, ReturnType, Args...>;
|
|
};
|
|
|
|
template <typename ReturnType, typename... Args>
|
|
struct FunctionTraits<ReturnType(Args...) const> {
|
|
using Call = ReturnType (*)(CallArg<Args>..., Data&);
|
|
using ConstSignature = ReturnType(Args...) const;
|
|
using NonConstSignature = ReturnType(Args...);
|
|
using OtherSignature = NonConstSignature;
|
|
|
|
template <typename F, typename R = CallableResult<const F&, Args...>>
|
|
using IfSafeResult = IfSafeResultImpl<R, ReturnType>;
|
|
|
|
template <typename Fun, bool Small>
|
|
static constexpr Call call =
|
|
call_<const Fun, Small, false, ReturnType, CallArg<Args>...>;
|
|
|
|
static ReturnType uninitCall(CallArg<Args>..., Data&) {
|
|
throw_exception<std::bad_function_call>();
|
|
}
|
|
|
|
ReturnType operator()(Args... args) const {
|
|
auto& fn = *static_cast<const Function<ConstSignature>*>(this);
|
|
return fn.call_(static_cast<Args&&>(args)..., fn.data_);
|
|
}
|
|
|
|
using SharedProxy =
|
|
FunctionTraitsSharedProxy<ConstSignature, false, ReturnType, Args...>;
|
|
};
|
|
|
|
template <typename ReturnType, typename... Args>
|
|
struct FunctionTraits<ReturnType(Args...) noexcept> {
|
|
using Call = ReturnType (*)(CallArg<Args>..., Data&) noexcept;
|
|
using ConstSignature = ReturnType(Args...) const noexcept;
|
|
using NonConstSignature = ReturnType(Args...) noexcept;
|
|
using OtherSignature = ConstSignature;
|
|
|
|
template <
|
|
typename F,
|
|
typename R = CallableResult<F&, Args...>,
|
|
std::enable_if_t<CallableNoexcept<F&, Args...>, int> = 0>
|
|
using IfSafeResult = IfSafeResultImpl<R, ReturnType>;
|
|
|
|
template <typename Fun, bool Small>
|
|
static constexpr Call call =
|
|
call_<Fun, Small, true, ReturnType, CallArg<Args>...>;
|
|
|
|
static ReturnType uninitCall(CallArg<Args>..., Data&) noexcept {
|
|
terminate_with<std::bad_function_call>();
|
|
}
|
|
|
|
ReturnType operator()(Args... args) noexcept {
|
|
auto& fn = *static_cast<Function<NonConstSignature>*>(this);
|
|
return fn.call_(static_cast<Args&&>(args)..., fn.data_);
|
|
}
|
|
|
|
using SharedProxy =
|
|
FunctionTraitsSharedProxy<NonConstSignature, true, ReturnType, Args...>;
|
|
};
|
|
|
|
template <typename ReturnType, typename... Args>
|
|
struct FunctionTraits<ReturnType(Args...) const noexcept> {
|
|
using Call = ReturnType (*)(CallArg<Args>..., Data&) noexcept;
|
|
using ConstSignature = ReturnType(Args...) const noexcept;
|
|
using NonConstSignature = ReturnType(Args...) noexcept;
|
|
using OtherSignature = NonConstSignature;
|
|
|
|
template <
|
|
typename F,
|
|
typename R = CallableResult<const F&, Args...>,
|
|
std::enable_if_t<CallableNoexcept<const F&, Args...>, int> = 0>
|
|
using IfSafeResult = IfSafeResultImpl<R, ReturnType>;
|
|
|
|
template <typename Fun, bool Small>
|
|
static constexpr Call call =
|
|
call_<const Fun, Small, true, ReturnType, CallArg<Args>...>;
|
|
|
|
static ReturnType uninitCall(CallArg<Args>..., Data&) noexcept {
|
|
terminate_with<std::bad_function_call>();
|
|
}
|
|
|
|
ReturnType operator()(Args... args) const noexcept {
|
|
auto& fn = *static_cast<const Function<ConstSignature>*>(this);
|
|
return fn.call_(static_cast<Args&&>(args)..., fn.data_);
|
|
}
|
|
|
|
using SharedProxy =
|
|
FunctionTraitsSharedProxy<ConstSignature, true, ReturnType, Args...>;
|
|
};
|
|
|
|
// These are control functions. They type-erase the operations of move-
|
|
// construction, destruction, and conversion to bool.
|
|
//
|
|
// The interface operations are noexcept, so the implementations are as well.
|
|
// Having the implementations be noexcept in the type permits callers to omit
|
|
// exception-handling machinery.
|
|
//
|
|
// This is intentionally instantiated per size rather than per function in order
|
|
// to minimize the number of instantiations. It would be safe to minimize
|
|
// instantiations even more by simply having a single non-template function that
|
|
// copies sizeof(Data) bytes rather than only copying sizeof(Fun) bytes, but
|
|
// then for small function types it would be likely to cross cache lines without
|
|
// need. But it is only necessary to handle those sizes which are multiples of
|
|
// the alignof(Data), and to round up other sizes.
|
|
struct DispatchSmallTrivial {
|
|
static constexpr bool is_in_situ = true;
|
|
static constexpr bool is_trivial = true;
|
|
|
|
template <std::size_t Size>
|
|
static std::size_t exec_(Op o, Data* src, Data* dst) noexcept {
|
|
switch (o) {
|
|
case Op::MOVE:
|
|
std::memcpy(static_cast<void*>(dst), static_cast<void*>(src), Size);
|
|
break;
|
|
case Op::NUKE:
|
|
break;
|
|
case Op::HEAP:
|
|
break;
|
|
}
|
|
return 0U;
|
|
}
|
|
template <std::size_t size, std::size_t adjust = alignof(Data) - 1>
|
|
static constexpr std::size_t size_ = (size + adjust) & ~adjust;
|
|
template <typename Fun>
|
|
static constexpr auto exec = exec_<size_<sizeof(Fun)>>;
|
|
};
|
|
|
|
struct DispatchBigTrivial {
|
|
static constexpr bool is_in_situ = false;
|
|
static constexpr bool is_trivial = true;
|
|
|
|
template <typename Fun, typename Base>
|
|
static constexpr auto call = Base::template callBig<Fun>;
|
|
|
|
static constexpr bool is_align_large(size_t align) {
|
|
return align > __STDCPP_DEFAULT_NEW_ALIGNMENT__;
|
|
}
|
|
|
|
template <bool IsAlignLarge>
|
|
static std::size_t exec_(Op o, Data* src, Data* dst) noexcept {
|
|
switch (o) {
|
|
case Op::MOVE:
|
|
dst->bigt = src->bigt;
|
|
src->bigt = {};
|
|
break;
|
|
case Op::NUKE:
|
|
IsAlignLarge
|
|
? operator_delete(
|
|
src->big, src->bigt.size, std::align_val_t(src->bigt.align))
|
|
: operator_delete(src->big, src->bigt.size);
|
|
break;
|
|
case Op::HEAP:
|
|
break;
|
|
}
|
|
return src->bigt.size;
|
|
}
|
|
template <typename T>
|
|
static constexpr auto exec = exec_<is_align_large(alignof(T))>;
|
|
|
|
FOLLY_ALWAYS_INLINE static void ctor(
|
|
Data& data,
|
|
void const* fun,
|
|
std::size_t size,
|
|
std::size_t align) noexcept {
|
|
// cannot use type-specific new since type-specific new is overrideable
|
|
// in concert with type-specific delete
|
|
data.bigt.big = is_align_large(align)
|
|
? operator_new(size, std::align_val_t(align))
|
|
: operator_new(size);
|
|
data.bigt.size = size;
|
|
data.bigt.align = align;
|
|
std::memcpy(data.bigt.big, fun, size);
|
|
}
|
|
};
|
|
|
|
struct DispatchSmall {
|
|
static constexpr bool is_in_situ = true;
|
|
static constexpr bool is_trivial = false;
|
|
|
|
template <typename Fun>
|
|
static std::size_t exec(Op o, Data* src, Data* dst) noexcept {
|
|
switch (o) {
|
|
case Op::MOVE:
|
|
::new (static_cast<void*>(&dst->tiny)) Fun(static_cast<Fun&&>(
|
|
*static_cast<Fun*>(static_cast<void*>(&src->tiny))));
|
|
[[fallthrough]];
|
|
case Op::NUKE:
|
|
static_cast<Fun*>(static_cast<void*>(&src->tiny))->~Fun();
|
|
break;
|
|
case Op::HEAP:
|
|
break;
|
|
}
|
|
return 0U;
|
|
}
|
|
};
|
|
|
|
struct DispatchBig {
|
|
static constexpr bool is_in_situ = false;
|
|
static constexpr bool is_trivial = false;
|
|
|
|
template <typename Fun>
|
|
static std::size_t exec(Op o, Data* src, Data* dst) noexcept {
|
|
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 sizeof(Fun);
|
|
}
|
|
};
|
|
|
|
template <bool InSitu, bool IsTriv>
|
|
struct Dispatch;
|
|
template <>
|
|
struct Dispatch<true, true> : DispatchSmallTrivial {};
|
|
template <>
|
|
struct Dispatch<true, false> : DispatchSmall {};
|
|
template <>
|
|
struct Dispatch<false, true> : DispatchBigTrivial {};
|
|
template <>
|
|
struct Dispatch<false, false> : DispatchBig {};
|
|
|
|
template <
|
|
typename Fun,
|
|
bool InSituSize = sizeof(Fun) <= sizeof(Data),
|
|
bool InSituAlign = alignof(Fun) <= alignof(Data),
|
|
bool InSituNoexcept = noexcept(Fun(FOLLY_DECLVAL(Fun)))>
|
|
using DispatchOf = Dispatch<
|
|
InSituSize && InSituAlign && InSituNoexcept,
|
|
std::is_trivially_copyable_v<Fun>>;
|
|
|
|
// This cannot be done inseide `Function` class, because the word
|
|
// `Function` there refers to the instantion and not the template.
|
|
template <typename T>
|
|
constexpr bool is_instantiation_of_folly_function_v =
|
|
is_instantiation_of_v<Function, T>;
|
|
|
|
} // 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 CoerceTag = detail::function::CoerceTag;
|
|
|
|
using Traits = detail::function::FunctionTraits<FunctionType>;
|
|
using Call = typename Traits::Call;
|
|
using Exec = std::size_t (*)(Op, Data*, Data*) noexcept;
|
|
|
|
// 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_{unsafe_default_initialized};
|
|
Call call_{&Traits::uninitCall};
|
|
Exec exec_{nullptr};
|
|
|
|
std::size_t exec(Op o, Data* src, Data* dst) const {
|
|
if (!exec_) {
|
|
return 0U;
|
|
}
|
|
return 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 Signature>
|
|
Function(Function<Signature>&& fun, CoerceTag) {
|
|
using Fun = Function<Signature>;
|
|
if (fun) {
|
|
data_.big = new Fun(static_cast<Fun&&>(fun));
|
|
call_ = Traits::template call<Fun, false>;
|
|
exec_ = Exec(detail::function::DispatchBig::exec<Fun>);
|
|
}
|
|
}
|
|
|
|
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.
|
|
*/
|
|
constexpr Function() = default;
|
|
|
|
// not copyable
|
|
Function(const Function&) = delete;
|
|
|
|
#ifdef __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 */ constexpr Function(std::nullptr_t) noexcept {}
|
|
|
|
/**
|
|
* Constructs a new `Function` from any callable object that is _not_ a
|
|
* `folly::Function`.
|
|
*
|
|
* \note `typename Traits::template IfSafeResult<Fun>` prevents this overload
|
|
* from being selected by overload resolution when `fun` is not a compatible
|
|
* function.
|
|
*
|
|
* \note The noexcept requires some explanation. `is_in_situ` 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 `is_in_situ`, 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.
|
|
*
|
|
* @param fun 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...`).
|
|
*/
|
|
template <
|
|
typename Fun,
|
|
typename = std::enable_if_t<
|
|
!detail::function::is_instantiation_of_folly_function_v<Fun>>,
|
|
typename = typename Traits::template IfSafeResult<Fun>>
|
|
/* implicit */ constexpr Function(Fun fun) noexcept(
|
|
detail::function::DispatchOf<Fun>::is_in_situ) {
|
|
using Dispatch = detail::function::DispatchOf<Fun>;
|
|
if constexpr (detail::function::IsNullptrCompatible<Fun>) {
|
|
if (detail::function::isEmptyFunction(fun)) {
|
|
return;
|
|
}
|
|
}
|
|
if constexpr (Dispatch::is_in_situ) {
|
|
if constexpr (
|
|
!std::is_empty<Fun>::value || !std::is_trivially_copyable_v<Fun>) {
|
|
::new (&data_.tiny) Fun(static_cast<Fun&&>(fun));
|
|
}
|
|
} else {
|
|
if constexpr (Dispatch::is_trivial) {
|
|
Dispatch::ctor(data_, &fun, sizeof(Fun), alignof(Fun));
|
|
} else {
|
|
data_.big = new Fun(static_cast<Fun&&>(fun));
|
|
}
|
|
}
|
|
call_ = Traits::template call<Fun, Dispatch::is_in_situ>;
|
|
exec_ = Exec(Dispatch::template exec<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 Fun = Function<Signature>,
|
|
// prevent gcc from making this a better match than move-ctor
|
|
typename = std::enable_if_t<!std::is_same<Function, Fun>::value>,
|
|
typename = typename Traits::template IfSafeResult<Fun>>
|
|
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;
|
|
|
|
#ifdef __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 {
|
|
exec(Op::NUKE, &data_, nullptr);
|
|
if (FOLLY_LIKELY(this != &that)) {
|
|
that.exec(Op::MOVE, &that.data_, &data_);
|
|
exec_ = that.exec_;
|
|
call_ = that.call_;
|
|
}
|
|
that.exec_ = nullptr;
|
|
that.call_ = &Traits::uninitCall;
|
|
return *this;
|
|
}
|
|
|
|
/**
|
|
* Assigns a callable object to this `Function`. If the operation fails,
|
|
* `*this` is left unmodified.
|
|
*
|
|
* \note `typename = decltype(Function(FOLLY_DECLVAL(Fun&&)))` prevents this
|
|
* overload from being selected by overload resolution when `fun` is not a
|
|
* compatible function.
|
|
*/
|
|
template <
|
|
typename Fun,
|
|
typename...,
|
|
bool Nx = noexcept(Function(FOLLY_DECLVAL(Fun&&)))>
|
|
Function& operator=(Fun fun) noexcept(Nx) {
|
|
// Doing this in place is more efficient when we can do so safely.
|
|
if (Nx) {
|
|
// 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 = typename Traits::template IfSafeResult<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`.
|
|
*
|
|
* @param that a folly::Function ref
|
|
*/
|
|
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 the size of the allocation made to store the callable on the
|
|
* heap. If `0` is returned, there has been no additional memory
|
|
* allocation because the callable is stored within the `Function` object.
|
|
*/
|
|
std::size_t heapAllocatedMemory() const noexcept {
|
|
return exec(Op::HEAP, &data_, 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);
|
|
}
|
|
|
|
/**
|
|
* Casts a `folly::Function` from non-const to a const signature.
|
|
*
|
|
* NOTE: 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 invocation of the function from a const context,
|
|
* in which case you do not need to use `constCastFunction` and just
|
|
* use a non-const `folly::Function`. Or, you may need invocation 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 invocation 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`.
|
|
*
|
|
* @param that a non-const folly::Function.
|
|
*/
|
|
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);
|
|
}
|
|
|
|
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);
|
|
}
|
|
|
|
namespace detail {
|
|
|
|
template <typename Void, typename>
|
|
struct function_ctor_deduce_;
|
|
|
|
template <typename P>
|
|
struct function_ctor_deduce_<
|
|
std::enable_if_t<std::is_function<std::remove_pointer_t<P>>::value>,
|
|
P> {
|
|
using type = std::remove_pointer_t<P>;
|
|
};
|
|
|
|
template <typename F>
|
|
struct function_ctor_deduce_<void_t<decltype(&F::operator())>, F> {
|
|
using type =
|
|
typename member_pointer_traits<decltype(&F::operator())>::member_type;
|
|
};
|
|
|
|
template <typename F>
|
|
using function_ctor_deduce_t = typename function_ctor_deduce_<void, F>::type;
|
|
|
|
} // namespace detail
|
|
|
|
template <typename F>
|
|
Function(F) -> Function<detail::function_ctor_deduce_t<F>>;
|
|
|
|
/**
|
|
* @class folly::FunctionRef
|
|
*
|
|
* 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 {
|
|
template <typename Arg>
|
|
using CallArg = detail::function::CallArg<Arg>;
|
|
|
|
using Call = ReturnType (*)(CallArg<Args>..., void*);
|
|
|
|
static ReturnType uninitCall(CallArg<Args>..., void*) {
|
|
throw_exception<std::bad_function_call>();
|
|
}
|
|
|
|
template <
|
|
typename Fun,
|
|
std::enable_if_t<!std::is_pointer<Fun>::value, int> = 0>
|
|
static ReturnType call(CallArg<Args>... args, void* object) {
|
|
using Pointer = std::add_pointer_t<Fun>;
|
|
return static_cast<ReturnType>(invoke(
|
|
static_cast<Fun&&>(*static_cast<Pointer>(object)),
|
|
static_cast<Args&&>(args)...));
|
|
}
|
|
template <
|
|
typename Fun,
|
|
std::enable_if_t<std::is_pointer<Fun>::value, int> = 0>
|
|
static ReturnType call(CallArg<Args>... args, void* object) {
|
|
return static_cast<ReturnType>(
|
|
invoke(reinterpret_cast<Fun>(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.
|
|
*/
|
|
constexpr FunctionRef() = default;
|
|
|
|
/**
|
|
* Like default constructor. Constructs an empty FunctionRef.
|
|
*
|
|
* Invoking it will throw std::bad_function_call.
|
|
*/
|
|
constexpr explicit FunctionRef(std::nullptr_t) noexcept {}
|
|
|
|
/**
|
|
* Construct a FunctionRef from a reference to a callable object. If the
|
|
* callable is considered to be an empty callable, the FunctionRef will be
|
|
* empty.
|
|
*/
|
|
template <
|
|
typename Fun,
|
|
std::enable_if_t<
|
|
Conjunction<
|
|
Negation<std::is_same<FunctionRef, std::decay_t<Fun>>>,
|
|
is_invocable_r<ReturnType, Fun&&, Args&&...>>::value,
|
|
int> = 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`
|
|
auto& ref = fun; // work around forwarding lint advice
|
|
if constexpr ( //
|
|
detail::function::IsNullptrCompatible<std::decay_t<Fun>>) {
|
|
if (detail::function::isEmptyFunction(fun)) {
|
|
return;
|
|
}
|
|
}
|
|
auto ptr = std::addressof(ref);
|
|
object_ = const_cast<void*>(static_cast<void const*>(ptr));
|
|
call_ = &FunctionRef::template call<Fun>;
|
|
}
|
|
|
|
/**
|
|
* Constructs a FunctionRef from a pointer to a function. If the
|
|
* pointer is nullptr, the FunctionRef will be empty.
|
|
*/
|
|
template <
|
|
typename Fun,
|
|
std::enable_if_t<std::is_function<Fun>::value, int> = 0,
|
|
std::enable_if_t<is_invocable_r_v<ReturnType, Fun&, Args&&...>, int> = 0>
|
|
constexpr /* implicit */ FunctionRef(Fun* fun) noexcept {
|
|
if (fun) {
|
|
object_ = const_cast<void*>(reinterpret_cast<void const*>(fun));
|
|
call_ = &FunctionRef::template call<Fun*>;
|
|
}
|
|
}
|
|
|
|
ReturnType operator()(Args... args) const {
|
|
return call_(static_cast<Args&&>(args)..., object_);
|
|
}
|
|
|
|
constexpr explicit operator bool() const noexcept { return object_; }
|
|
|
|
constexpr friend bool operator==(
|
|
FunctionRef<ReturnType(Args...)> ref, std::nullptr_t) noexcept {
|
|
return ref.object_ == nullptr;
|
|
}
|
|
constexpr friend bool operator!=(
|
|
FunctionRef<ReturnType(Args...)> ref, std::nullptr_t) noexcept {
|
|
return ref.object_ != nullptr;
|
|
}
|
|
|
|
constexpr friend bool operator==(
|
|
std::nullptr_t, FunctionRef<ReturnType(Args...)> ref) noexcept {
|
|
return ref.object_ == nullptr;
|
|
}
|
|
constexpr friend bool operator!=(
|
|
std::nullptr_t, FunctionRef<ReturnType(Args...)> ref) noexcept {
|
|
return ref.object_ != nullptr;
|
|
}
|
|
};
|
|
|
|
} // namespace folly
|