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