1089 lines
37 KiB
C++
1089 lines
37 KiB
C++
/*
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* Copyright (c) Facebook, Inc. and its affiliates.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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/*
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* @author Eric Niebler (eniebler@fb.com), Sven Over (over@fb.com)
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* Acknowledgements: Giuseppe Ottaviano (ott@fb.com)
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*/
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/**
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* @class Function
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*
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* @brief A polymorphic function wrapper that is not copyable and does not
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* require the wrapped function to be copy constructible.
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*
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* `folly::Function` is a polymorphic function wrapper, similar to
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* `std::function`. The template parameters of the `folly::Function` define
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* the parameter signature of the wrapped callable, but not the specific
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* type of the embedded callable. E.g. a `folly::Function<int(int)>`
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* can wrap callables that return an `int` when passed an `int`. This can be a
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* function pointer or any class object implementing one or both of
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*
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* int operator(int);
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* int operator(int) const;
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*
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* If both are defined, the non-const one takes precedence.
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*
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* Unlike `std::function`, a `folly::Function` can wrap objects that are not
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* copy constructible. As a consequence of this, `folly::Function` itself
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* is not copyable, either.
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*
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* Another difference is that, unlike `std::function`, `folly::Function` treats
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* const-ness of methods correctly. While a `std::function` allows to wrap
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* an object that only implements a non-const `operator()` and invoke
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* a const-reference of the `std::function`, `folly::Function` requires you to
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* declare a function type as const in order to be able to execute it on a
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* const-reference.
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*
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* For example:
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*
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* class Foo {
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* public:
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* void operator()() {
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* // mutates the Foo object
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* }
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* };
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*
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* class Bar {
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* std::function<void(void)> foo_; // wraps a Foo object
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* public:
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* void mutateFoo() const
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* {
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* foo_();
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* }
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* };
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*
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* Even though `mutateFoo` is a const-method, so it can only reference `foo_`
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* as const, it is able to call the non-const `operator()` of the Foo
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* object that is embedded in the foo_ function.
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*
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* `folly::Function` will not allow you to do that. You will have to decide
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* whether you need to invoke your wrapped callable from a const reference
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* (like in the example above), in which case it will only wrap a
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* `operator() const`. If your functor does not implement that,
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* compilation will fail. If you do not require to be able to invoke the
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* wrapped function in a const context, you can wrap any functor that
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* implements either or both of const and non-const `operator()`.
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*
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* The template parameter of `folly::Function`, the `FunctionType`, can be
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* const-qualified. Be aware that the const is part of the function signature.
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* It does not mean that the function type is a const type.
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*
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* using FunctionType = R(Args...);
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* using ConstFunctionType = R(Args...) const;
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*
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* In this example, `FunctionType` and `ConstFunctionType` are different
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* types. `ConstFunctionType` is not the same as `const FunctionType`.
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* As a matter of fact, trying to use the latter should emit a compiler
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* warning or error, because it has no defined meaning.
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*
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* // This will not compile:
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* folly::Function<void(void) const> func = Foo();
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* // because Foo does not have a member function of the form:
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* // void operator()() const;
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*
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* // This will compile just fine:
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* folly::Function<void(void)> func = Foo();
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* // and it will wrap the existing member function:
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* // void operator()();
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*
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* When should a const function type be used? As a matter of fact, you will
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* probably not need to use const function types very often. See the following
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* example:
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*
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* class Bar {
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* folly::Function<void()> func_;
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* folly::Function<void() const> constFunc_;
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*
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* void someMethod() {
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* // Can call func_.
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* func_();
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* // Can call constFunc_.
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* constFunc_();
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* }
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*
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* void someConstMethod() const {
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* // Can call constFunc_.
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* constFunc_();
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* // However, cannot call func_ because a non-const method cannot
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* // be called from a const one.
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* }
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* };
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*
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* As you can see, whether the `folly::Function`'s function type should
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* be declared const or not is identical to whether a corresponding method
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* would be declared const or not.
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*
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* You only require a `folly::Function` to hold a const function type, if you
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* intend to invoke it from within a const context. This is to ensure that
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* you cannot mutate its inner state when calling in a const context.
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*
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* This is how the const/non-const choice relates to lambda functions:
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*
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* // Non-mutable lambdas: can be stored in a non-const...
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* folly::Function<void(int)> print_number =
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* [] (int number) { std::cout << number << std::endl; };
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*
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* // ...as well as in a const folly::Function
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* folly::Function<void(int) const> print_number_const =
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* [] (int number) { std::cout << number << std::endl; };
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*
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* // Mutable lambda: can only be stored in a non-const folly::Function:
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* int number = 0;
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* folly::Function<void()> print_number =
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* [number] () mutable { std::cout << ++number << std::endl; };
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* // Trying to store the above mutable lambda in a
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* // `folly::Function<void() const>` would lead to a compiler error:
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* // error: no viable conversion from '(lambda at ...)' to
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* // 'folly::Function<void () const>'
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*
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* Casting between const and non-const `folly::Function`s:
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* conversion from const to non-const signatures happens implicitly. Any
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* function that takes a `folly::Function<R(Args...)>` can be passed
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* a `folly::Function<R(Args...) const>` without explicit conversion.
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* This is safe, because casting from const to non-const only entails giving
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* up the ability to invoke the function from a const context.
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* Casting from a non-const to a const signature is potentially dangerous,
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* as it means that a function that may change its inner state when invoked
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* is made possible to call from a const context. Therefore this cast does
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* not happen implicitly. The function `folly::constCastFunction` can
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* be used to perform the cast.
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*
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* // Mutable lambda: can only be stored in a non-const folly::Function:
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* int number = 0;
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* folly::Function<void()> print_number =
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* [number] () mutable { std::cout << ++number << std::endl; };
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*
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* // const-cast to a const folly::Function:
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* folly::Function<void() const> print_number_const =
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* constCastFunction(std::move(print_number));
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*
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* When to use const function types?
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* Generally, only when you need them. When you use a `folly::Function` as a
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* member of a struct or class, only use a const function signature when you
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* need to invoke the function from const context.
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* When passing a `folly::Function` to a function, the function should accept
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* a non-const `folly::Function` whenever possible, i.e. when it does not
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* need to pass on or store a const `folly::Function`. This is the least
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* possible constraint: you can always pass a const `folly::Function` when
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* the function accepts a non-const one.
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*
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* How does the const behaviour compare to `std::function`?
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* `std::function` can wrap object with non-const invocation behaviour but
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* exposes them as const. The equivalent behaviour can be achieved with
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* `folly::Function` like so:
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*
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* std::function<void(void)> stdfunc = someCallable;
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*
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* folly::Function<void(void) const> uniqfunc = constCastFunction(
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* folly::Function<void(void)>(someCallable)
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* );
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*
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* You need to wrap the callable first in a non-const `folly::Function` to
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* select a non-const invoke operator (or the const one if no non-const one is
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* present), and then move it into a const `folly::Function` using
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* `constCastFunction`.
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* The name of `constCastFunction` should warn you that something
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* potentially dangerous is happening. As a matter of fact, using
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* `std::function` always involves this potentially dangerous aspect, which
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* is why it is not considered fully const-safe or even const-correct.
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* However, in most of the cases you will not need the dangerous aspect at all.
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* Either you do not require invocation of the function from a const context,
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* in which case you do not need to use `constCastFunction` and just
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* use the inner `folly::Function` in the example above, i.e. just use a
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* non-const `folly::Function`. Or, you may need invocation from const, but
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* the callable you are wrapping does not mutate its state (e.g. it is a class
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* object and implements `operator() const`, or it is a normal,
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* non-mutable lambda), in which case you can wrap the callable in a const
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* `folly::Function` directly, without using `constCastFunction`.
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* Only if you require invocation from a const context of a callable that
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* may mutate itself when invoked you have to go through the above procedure.
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* However, in that case what you do is potentially dangerous and requires
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* the equivalent of a `const_cast`, hence you need to call
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* `constCastFunction`.
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*/
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#pragma once
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#include <functional>
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#include <memory>
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#include <new>
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#include <type_traits>
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#include <utility>
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#include <folly/CppAttributes.h>
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#include <folly/Portability.h>
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#include <folly/Traits.h>
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#include <folly/functional/Invoke.h>
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#include <folly/lang/Exception.h>
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namespace folly {
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template <typename FunctionType>
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class Function;
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template <typename ReturnType, typename... Args>
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Function<ReturnType(Args...) const> constCastFunction(
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Function<ReturnType(Args...)>&&) noexcept;
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#if FOLLY_HAVE_NOEXCEPT_FUNCTION_TYPE
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template <typename ReturnType, typename... Args>
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Function<ReturnType(Args...) const noexcept> constCastFunction(
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Function<ReturnType(Args...) noexcept>&&) noexcept;
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#endif
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namespace detail {
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namespace function {
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enum class Op { MOVE, NUKE, HEAP };
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union Data {
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Data() {}
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void* big;
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std::aligned_storage<6 * sizeof(void*)>::type tiny;
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};
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template <typename Fun, typename = Fun*>
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using IsSmall = Conjunction<
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bool_constant<(sizeof(Fun) <= sizeof(Data::tiny))>,
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std::is_nothrow_move_constructible<Fun>>;
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using SmallTag = std::true_type;
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using HeapTag = std::false_type;
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template <typename T>
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struct NotFunction : std::true_type {};
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template <typename T>
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struct NotFunction<Function<T>> : std::false_type {};
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template <typename T>
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using EnableIfNotFunction =
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typename std::enable_if<NotFunction<T>::value>::type;
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struct CoerceTag {};
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template <typename, typename T>
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struct IsFunctionNullptrTestable : std::false_type {};
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template <typename T>
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struct IsFunctionNullptrTestable<
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void_t<decltype(
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static_cast<bool>(static_cast<T const&>(T(nullptr)) == nullptr))>,
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T> : std::true_type {};
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template <typename T>
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constexpr std::enable_if_t< //
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!IsFunctionNullptrTestable<void, T>::value,
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std::false_type>
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isEmptyFunction(T const&) {
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return {};
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}
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template <typename T>
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constexpr std::enable_if_t<IsFunctionNullptrTestable<void, T>::value, bool>
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isEmptyFunction(T const& t) {
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return static_cast<bool>(t == nullptr);
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}
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template <typename F, typename... Args>
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using CallableResult = decltype(std::declval<F>()(std::declval<Args>()...));
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template <
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typename From,
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typename To,
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typename = typename std::enable_if<
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!std::is_reference<To>::value || std::is_reference<From>::value>::type>
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using SafeResultOf = decltype(static_cast<To>(std::declval<From>()));
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#if defined(_MSC_VER)
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// Need a workaround for MSVC to avoid the inscrutable error:
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//
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// folly\function.h(...) : fatal error C1001: An internal error has
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// occurred in the compiler.
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// (compiler file 'f:\dd\vctools\compiler\utc\src\p2\main.c', line 258)
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// To work around this problem, try simplifying or changing the program
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// near the locations listed above.
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template <typename T>
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using CallArg = T&&;
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#else
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template <typename T>
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using CallArg = conditional_t<is_trivially_copyable<T>::value, T, T&&>;
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#endif
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template <typename F, typename R, typename... A>
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class FunctionTraitsSharedProxy {
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std::shared_ptr<Function<F>> sp_;
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public:
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explicit FunctionTraitsSharedProxy(std::nullptr_t) noexcept {}
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explicit FunctionTraitsSharedProxy(Function<F>&& func)
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: sp_(func ? std::make_shared<Function<F>>(std::move(func))
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: std::shared_ptr<Function<F>>()) {}
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R operator()(A&&... args) const {
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if (!sp_) {
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throw_exception<std::bad_function_call>();
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}
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return (*sp_)(static_cast<A&&>(args)...);
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}
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explicit operator bool() const noexcept {
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return sp_ != nullptr;
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}
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friend bool operator==(
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FunctionTraitsSharedProxy<F, R, A...> const& proxy,
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std::nullptr_t) noexcept {
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return proxy.sp_ == nullptr;
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}
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friend bool operator!=(
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FunctionTraitsSharedProxy<F, R, A...> const& proxy,
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std::nullptr_t) noexcept {
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return proxy.sp_ != nullptr;
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}
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friend bool operator==(
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std::nullptr_t,
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FunctionTraitsSharedProxy<F, R, A...> const& proxy) noexcept {
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return proxy.sp_ == nullptr;
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}
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friend bool operator!=(
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std::nullptr_t,
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FunctionTraitsSharedProxy<F, R, A...> const& proxy) noexcept {
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return proxy.sp_ != nullptr;
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}
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};
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template <typename FunctionType>
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struct FunctionTraits;
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template <typename ReturnType, typename... Args>
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struct FunctionTraits<ReturnType(Args...)> {
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using Call = ReturnType (*)(CallArg<Args>..., Data&);
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using IsConst = std::false_type;
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using ConstSignature = ReturnType(Args...) const;
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using NonConstSignature = ReturnType(Args...);
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using OtherSignature = ConstSignature;
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template <typename F>
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using ResultOf =
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SafeResultOf<CallableResult<std::decay_t<F>&, Args...>, ReturnType>;
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template <typename Fun>
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static ReturnType callSmall(CallArg<Args>... args, Data& p) {
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auto& fn = *static_cast<Fun*>(static_cast<void*>(&p.tiny));
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#if __cpp_if_constexpr >= 201606L
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if constexpr (std::is_void<ReturnType>::value) {
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fn(static_cast<Args&&>(args)...);
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} else {
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return fn(static_cast<Args&&>(args)...);
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}
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#else
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return static_cast<ReturnType>(fn(static_cast<Args&&>(args)...));
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#endif
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}
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template <typename Fun>
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static ReturnType callBig(CallArg<Args>... args, Data& p) {
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auto& fn = *static_cast<Fun*>(p.big);
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#if __cpp_if_constexpr >= 201606L
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if constexpr (std::is_void<ReturnType>::value) {
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fn(static_cast<Args&&>(args)...);
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} else {
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return fn(static_cast<Args&&>(args)...);
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}
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#else
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return static_cast<ReturnType>(fn(static_cast<Args&&>(args)...));
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#endif
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}
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static ReturnType uninitCall(CallArg<Args>..., Data&) {
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throw_exception<std::bad_function_call>();
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}
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ReturnType operator()(Args... args) {
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auto& fn = *static_cast<Function<NonConstSignature>*>(this);
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return fn.call_(static_cast<Args&&>(args)..., fn.data_);
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}
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using SharedProxy =
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FunctionTraitsSharedProxy<NonConstSignature, ReturnType, Args...>;
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};
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|
template <typename ReturnType, typename... Args>
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|
struct FunctionTraits<ReturnType(Args...) const> {
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using Call = ReturnType (*)(CallArg<Args>..., Data&);
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using IsConst = std::true_type;
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using ConstSignature = ReturnType(Args...) const;
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using NonConstSignature = ReturnType(Args...);
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using OtherSignature = NonConstSignature;
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template <typename F>
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using ResultOf =
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SafeResultOf<CallableResult<const std::decay_t<F>&, Args...>, ReturnType>;
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|
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template <typename Fun>
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|
static ReturnType callSmall(CallArg<Args>... args, Data& p) {
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|
auto& fn = *static_cast<const Fun*>(static_cast<void*>(&p.tiny));
|
|
#if __cpp_if_constexpr >= 201606L
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|
if constexpr (std::is_void<ReturnType>::value) {
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fn(static_cast<Args&&>(args)...);
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} else {
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return fn(static_cast<Args&&>(args)...);
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}
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#else
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return static_cast<ReturnType>(fn(static_cast<Args&&>(args)...));
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#endif
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}
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template <typename Fun>
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static ReturnType callBig(CallArg<Args>... args, Data& p) {
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auto& fn = *static_cast<const Fun*>(p.big);
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|
#if __cpp_if_constexpr >= 201606L
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|
if constexpr (std::is_void<ReturnType>::value) {
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fn(static_cast<Args&&>(args)...);
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} else {
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return fn(static_cast<Args&&>(args)...);
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}
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#else
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return static_cast<ReturnType>(fn(static_cast<Args&&>(args)...));
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#endif
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}
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static ReturnType uninitCall(CallArg<Args>..., Data&) {
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throw_exception<std::bad_function_call>();
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}
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ReturnType operator()(Args... args) const {
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|
auto& fn = *static_cast<const Function<ConstSignature>*>(this);
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return fn.call_(static_cast<Args&&>(args)..., fn.data_);
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}
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using SharedProxy =
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FunctionTraitsSharedProxy<ConstSignature, ReturnType, Args...>;
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};
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|
|
#if FOLLY_HAVE_NOEXCEPT_FUNCTION_TYPE
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|
template <typename ReturnType, typename... Args>
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|
struct FunctionTraits<ReturnType(Args...) noexcept> {
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|
using Call = ReturnType (*)(CallArg<Args>..., Data&) 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<std::decay_t<F>&, Args...>, ReturnType>;
|
|
|
|
template <typename Fun>
|
|
static ReturnType callSmall(CallArg<Args>... args, Data& p) noexcept {
|
|
auto& fn = *static_cast<Fun*>(static_cast<void*>(&p.tiny));
|
|
#if __cpp_if_constexpr >= 201606L
|
|
if constexpr (std::is_void<ReturnType>::value) {
|
|
fn(static_cast<Args&&>(args)...);
|
|
} else {
|
|
return fn(static_cast<Args&&>(args)...);
|
|
}
|
|
#else
|
|
return static_cast<ReturnType>(fn(static_cast<Args&&>(args)...));
|
|
#endif
|
|
}
|
|
|
|
template <typename Fun>
|
|
static ReturnType callBig(CallArg<Args>... args, Data& p) noexcept {
|
|
auto& fn = *static_cast<Fun*>(p.big);
|
|
#if __cpp_if_constexpr >= 201606L
|
|
if constexpr (std::is_void<ReturnType>::value) {
|
|
fn(static_cast<Args&&>(args)...);
|
|
} else {
|
|
return fn(static_cast<Args&&>(args)...);
|
|
}
|
|
#else
|
|
return static_cast<ReturnType>(fn(static_cast<Args&&>(args)...));
|
|
#endif
|
|
}
|
|
|
|
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, ReturnType, Args...>;
|
|
};
|
|
|
|
template <typename ReturnType, typename... Args>
|
|
struct FunctionTraits<ReturnType(Args...) const noexcept> {
|
|
using Call = ReturnType (*)(CallArg<Args>..., Data&) 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 std::decay_t<F>&, Args...>, ReturnType>;
|
|
|
|
template <typename Fun>
|
|
static ReturnType callSmall(CallArg<Args>... args, Data& p) noexcept {
|
|
auto& fn = *static_cast<const Fun*>(static_cast<void*>(&p.tiny));
|
|
#if __cpp_if_constexpr >= 201606L
|
|
if constexpr (std::is_void<ReturnType>::value) {
|
|
fn(static_cast<Args&&>(args)...);
|
|
} else {
|
|
return fn(static_cast<Args&&>(args)...);
|
|
}
|
|
#else
|
|
return static_cast<ReturnType>(fn(static_cast<Args&&>(args)...));
|
|
#endif
|
|
}
|
|
|
|
template <typename Fun>
|
|
static ReturnType callBig(CallArg<Args>... args, Data& p) noexcept {
|
|
auto& fn = *static_cast<const Fun*>(p.big);
|
|
#if __cpp_if_constexpr >= 201606L
|
|
if constexpr (std::is_void<ReturnType>::value) {
|
|
fn(static_cast<Args&&>(args)...);
|
|
} else {
|
|
return fn(static_cast<Args&&>(args)...);
|
|
}
|
|
#else
|
|
return static_cast<ReturnType>(fn(static_cast<Args&&>(args)...));
|
|
#endif
|
|
}
|
|
|
|
static ReturnType uninitCall(CallArg<Args>..., Data&) noexcept {
|
|
throw_exception<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, ReturnType, Args...>;
|
|
};
|
|
#endif
|
|
|
|
template <typename Fun>
|
|
std::size_t 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 0U;
|
|
}
|
|
|
|
template <typename Fun>
|
|
std::size_t 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 sizeof(Fun);
|
|
}
|
|
|
|
} // 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 = std::size_t (*)(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};
|
|
|
|
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 Fun>
|
|
Function(Fun&& fun, SmallTag) noexcept {
|
|
using FunT = typename std::decay<Fun>::type;
|
|
if (!detail::function::isEmptyFunction(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;
|
|
if (!detail::function::isEmptyFunction(fun)) {
|
|
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 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, 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.
|
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* A folly::FunctionRef is cheap to construct as it contains only a pointer to
|
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* the referenced callable and a pointer to a function which invokes the
|
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* 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>;
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|
|
|
using Call = ReturnType (*)(CallArg<Args>..., void*);
|
|
|
|
static ReturnType uninitCall(CallArg<Args>..., void*) {
|
|
throw_exception<std::bad_function_call>();
|
|
}
|
|
|
|
template <typename Fun>
|
|
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)...));
|
|
}
|
|
|
|
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.
|
|
*/
|
|
template <
|
|
typename Fun,
|
|
typename std::enable_if<
|
|
Conjunction<
|
|
Negation<std::is_same<FunctionRef, std::decay_t<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::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
|