| // Copyright 2020 The Chromium Authors |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| #ifndef BASE_FUNCTIONAL_INVOKE_H_ |
| #define BASE_FUNCTIONAL_INVOKE_H_ |
| |
| #include <type_traits> |
| #include <utility> |
| |
| namespace gurl_base { |
| |
| namespace internal { |
| |
| // Helper struct and alias to deduce the class type from a member function |
| // pointer or member object pointer. |
| template <typename DecayedF> |
| struct member_pointer_class {}; |
| |
| template <typename ReturnT, typename ClassT> |
| struct member_pointer_class<ReturnT ClassT::*> { |
| using type = ClassT; |
| }; |
| |
| template <typename DecayedF> |
| using member_pointer_class_t = typename member_pointer_class<DecayedF>::type; |
| |
| // Utility struct to detect specializations of std::reference_wrapper. |
| template <typename T> |
| struct is_reference_wrapper : std::false_type {}; |
| |
| template <typename T> |
| struct is_reference_wrapper<std::reference_wrapper<T>> : std::true_type {}; |
| |
| // Small helpers used below in internal::invoke to make the SFINAE more concise. |
| template <typename F> |
| const bool& IsMemFunPtr = |
| std::is_member_function_pointer<std::decay_t<F>>::value; |
| |
| template <typename F> |
| const bool& IsMemObjPtr = std::is_member_object_pointer<std::decay_t<F>>::value; |
| |
| template <typename F, |
| typename T, |
| typename MemPtrClass = member_pointer_class_t<std::decay_t<F>>> |
| const bool& IsMemPtrToBaseOf = |
| std::is_base_of<MemPtrClass, std::decay_t<T>>::value; |
| |
| template <typename T> |
| const bool& IsRefWrapper = is_reference_wrapper<std::decay_t<T>>::value; |
| |
| template <bool B> |
| using EnableIf = std::enable_if_t<B, bool>; |
| |
| // Invokes a member function pointer on a reference to an object of a suitable |
| // type. Covers bullet 1 of the INVOKE definition. |
| // |
| // Reference: https://wg21.link/func.require#1.1 |
| template <typename F, |
| typename T1, |
| typename... Args, |
| EnableIf<IsMemFunPtr<F> && IsMemPtrToBaseOf<F, T1>> = true> |
| constexpr decltype(auto) InvokeImpl(F&& f, T1&& t1, Args&&... args) { |
| return (std::forward<T1>(t1).*f)(std::forward<Args>(args)...); |
| } |
| |
| // Invokes a member function pointer on a std::reference_wrapper to an object of |
| // a suitable type. Covers bullet 2 of the INVOKE definition. |
| // |
| // Reference: https://wg21.link/func.require#1.2 |
| template <typename F, |
| typename T1, |
| typename... Args, |
| EnableIf<IsMemFunPtr<F> && IsRefWrapper<T1>> = true> |
| constexpr decltype(auto) InvokeImpl(F&& f, T1&& t1, Args&&... args) { |
| return (t1.get().*f)(std::forward<Args>(args)...); |
| } |
| |
| // Invokes a member function pointer on a pointer-like type to an object of a |
| // suitable type. Covers bullet 3 of the INVOKE definition. |
| // |
| // Reference: https://wg21.link/func.require#1.3 |
| template <typename F, |
| typename T1, |
| typename... Args, |
| EnableIf<IsMemFunPtr<F> && !IsMemPtrToBaseOf<F, T1> && |
| !IsRefWrapper<T1>> = true> |
| constexpr decltype(auto) InvokeImpl(F&& f, T1&& t1, Args&&... args) { |
| return ((*std::forward<T1>(t1)).*f)(std::forward<Args>(args)...); |
| } |
| |
| // Invokes a member object pointer on a reference to an object of a suitable |
| // type. Covers bullet 4 of the INVOKE definition. |
| // |
| // Reference: https://wg21.link/func.require#1.4 |
| template <typename F, |
| typename T1, |
| EnableIf<IsMemObjPtr<F> && IsMemPtrToBaseOf<F, T1>> = true> |
| constexpr decltype(auto) InvokeImpl(F&& f, T1&& t1) { |
| return std::forward<T1>(t1).*f; |
| } |
| |
| // Invokes a member object pointer on a std::reference_wrapper to an object of |
| // a suitable type. Covers bullet 5 of the INVOKE definition. |
| // |
| // Reference: https://wg21.link/func.require#1.5 |
| template <typename F, |
| typename T1, |
| EnableIf<IsMemObjPtr<F> && IsRefWrapper<T1>> = true> |
| constexpr decltype(auto) InvokeImpl(F&& f, T1&& t1) { |
| return t1.get().*f; |
| } |
| |
| // Invokes a member object pointer on a pointer-like type to an object of a |
| // suitable type. Covers bullet 6 of the INVOKE definition. |
| // |
| // Reference: https://wg21.link/func.require#1.6 |
| template <typename F, |
| typename T1, |
| EnableIf<IsMemObjPtr<F> && !IsMemPtrToBaseOf<F, T1> && |
| !IsRefWrapper<T1>> = true> |
| constexpr decltype(auto) InvokeImpl(F&& f, T1&& t1) { |
| return (*std::forward<T1>(t1)).*f; |
| } |
| |
| // Invokes a regular function or function object. Covers bullet 7 of the INVOKE |
| // definition. |
| // |
| // Reference: https://wg21.link/func.require#1.7 |
| template <typename F, typename... Args> |
| constexpr decltype(auto) InvokeImpl(F&& f, Args&&... args) { |
| return std::forward<F>(f)(std::forward<Args>(args)...); |
| } |
| |
| } // namespace internal |
| |
| // Implementation of C++17's std::invoke. This is not based on implementation |
| // referenced in original std::invoke proposal, but rather a manual |
| // implementation, so that it can be constexpr. |
| // |
| // References: |
| // - https://wg21.link/n4169#implementability |
| // - https://en.cppreference.com/w/cpp/utility/functional/invoke |
| // - https://wg21.link/func.invoke |
| template <typename F, typename... Args> |
| constexpr decltype(auto) invoke(F&& f, Args&&... args) { |
| return internal::InvokeImpl(std::forward<F>(f), std::forward<Args>(args)...); |
| } |
| |
| } // namespace base |
| |
| #endif // BASE_FUNCTIONAL_INVOKE_H_ |