Repo created

TMessagesProj/jni/voip/webrtc/rtc_base/containers/invoke.h

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+/*
+ *  Copyright (c) 2021 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+// This implementation is borrowed from Chromium.
+
+#ifndef RTC_BASE_CONTAINERS_INVOKE_H_
+#define RTC_BASE_CONTAINERS_INVOKE_H_
+
+#include <type_traits>
+#include <utility>
+
+namespace webrtc {
+
+namespace invoke_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 invoke_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 invoke_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 invoke_internal::InvokeImpl(std::forward<F>(f),
+                                     std::forward<Args>(args)...);
+}
+
+}  // namespace webrtc
+
+#endif  // RTC_BASE_CONTAINERS_INVOKE_H_