| // Copyright (c) 2012 The Chromium Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| // |
| // NOTE: Header files that do not require the full definition of Callback or |
| // Closure should #include "base/callback_forward.h" instead of this file. |
| |
| #ifndef BASE_CALLBACK_H_ |
| #define BASE_CALLBACK_H_ |
| |
| #include "base/callback_forward.h" |
| #include "base/callback_internal.h" |
| |
| // ----------------------------------------------------------------------------- |
| // Usage documentation |
| // ----------------------------------------------------------------------------- |
| // |
| // Overview: |
| // A callback is similar in concept to a function pointer: it wraps a runnable |
| // object such as a function, method, lambda, or even another callback, allowing |
| // the runnable object to be invoked later via the callback object. |
| // |
| // Unlike function pointers, callbacks are created with base::BindOnce() or |
| // base::BindRepeating() and support partial function application. |
| // |
| // A base::OnceCallback may be Run() at most once; a base::RepeatingCallback may |
| // be Run() any number of times. |is_null()| is guaranteed to return true for a |
| // moved-from callback. |
| // |
| // // The lambda takes two arguments, but the first argument |x| is bound at |
| // // callback creation. |
| // base::OnceCallback<int(int)> cb = base::BindOnce([] (int x, int y) { |
| // return x + y; |
| // }, 1); |
| // // Run() only needs the remaining unbound argument |y|. |
| // printf("1 + 2 = %d\n", std::move(cb).Run(2)); // Prints 3 |
| // printf("cb is null? %s\n", |
| // cb.is_null() ? "true" : "false"); // Prints true |
| // std::move(cb).Run(2); // Crashes since |cb| has already run. |
| // |
| // Callbacks also support cancellation. A common use is binding the receiver |
| // object as a WeakPtr<T>. If that weak pointer is invalidated, calling Run() |
| // will be a no-op. Note that |is_cancelled()| and |is_null()| are distinct: |
| // simply cancelling a callback will not also make it null. |
| // |
| // base::Callback is currently a type alias for base::RepeatingCallback. In the |
| // future, we expect to flip this to default to base::OnceCallback. |
| // |
| // See //docs/callback.md for the full documentation. |
| |
| namespace base { |
| |
| template <typename R, typename... Args> |
| class OnceCallback<R(Args...)> : public internal::CallbackBase { |
| public: |
| using RunType = R(Args...); |
| using PolymorphicInvoke = R (*)(internal::BindStateBase*, |
| internal::PassingTraitsType<Args>...); |
| |
| constexpr OnceCallback() = default; |
| |
| explicit OnceCallback(internal::BindStateBase* bind_state) |
| : internal::CallbackBase(bind_state) {} |
| |
| OnceCallback(const OnceCallback&) = delete; |
| OnceCallback& operator=(const OnceCallback&) = delete; |
| |
| OnceCallback(OnceCallback&&) noexcept = default; |
| OnceCallback& operator=(OnceCallback&&) noexcept = default; |
| |
| OnceCallback(RepeatingCallback<RunType> other) |
| : internal::CallbackBase(std::move(other)) {} |
| |
| OnceCallback& operator=(RepeatingCallback<RunType> other) { |
| static_cast<internal::CallbackBase&>(*this) = std::move(other); |
| return *this; |
| } |
| |
| bool Equals(const OnceCallback& other) const { return EqualsInternal(other); } |
| |
| R Run(Args... args) const& { |
| static_assert(!sizeof(*this), |
| "OnceCallback::Run() may only be invoked on a non-const " |
| "rvalue, i.e. std::move(callback).Run()."); |
| NOTREACHED(); |
| } |
| |
| R Run(Args... args) && { |
| // Move the callback instance into a local variable before the invocation, |
| // that ensures the internal state is cleared after the invocation. |
| // It's not safe to touch |this| after the invocation, since running the |
| // bound function may destroy |this|. |
| OnceCallback cb = std::move(*this); |
| PolymorphicInvoke f = |
| reinterpret_cast<PolymorphicInvoke>(cb.polymorphic_invoke()); |
| return f(cb.bind_state_.get(), std::forward<Args>(args)...); |
| } |
| }; |
| |
| template <typename R, typename... Args> |
| class RepeatingCallback<R(Args...)> : public internal::CallbackBaseCopyable { |
| public: |
| using RunType = R(Args...); |
| using PolymorphicInvoke = R (*)(internal::BindStateBase*, |
| internal::PassingTraitsType<Args>...); |
| |
| constexpr RepeatingCallback() = default; |
| |
| explicit RepeatingCallback(internal::BindStateBase* bind_state) |
| : internal::CallbackBaseCopyable(bind_state) {} |
| |
| // Copyable and movable. |
| RepeatingCallback(const RepeatingCallback&) = default; |
| RepeatingCallback& operator=(const RepeatingCallback&) = default; |
| RepeatingCallback(RepeatingCallback&&) noexcept = default; |
| RepeatingCallback& operator=(RepeatingCallback&&) noexcept = default; |
| |
| bool Equals(const RepeatingCallback& other) const { |
| return EqualsInternal(other); |
| } |
| |
| R Run(Args... args) const& { |
| PolymorphicInvoke f = |
| reinterpret_cast<PolymorphicInvoke>(this->polymorphic_invoke()); |
| return f(this->bind_state_.get(), std::forward<Args>(args)...); |
| } |
| |
| R Run(Args... args) && { |
| // Move the callback instance into a local variable before the invocation, |
| // that ensures the internal state is cleared after the invocation. |
| // It's not safe to touch |this| after the invocation, since running the |
| // bound function may destroy |this|. |
| RepeatingCallback cb = std::move(*this); |
| PolymorphicInvoke f = |
| reinterpret_cast<PolymorphicInvoke>(cb.polymorphic_invoke()); |
| return f(cb.bind_state_.get(), std::forward<Args>(args)...); |
| } |
| }; |
| |
| } // namespace base |
| |
| #endif // BASE_CALLBACK_H_ |