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+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// absl::base_internal::Invoke(f, args...) is an implementation of
+// INVOKE(f, args...) from section [func.require] of the C++ standard.
+//
+// [func.require]
+// Define INVOKE (f, t1, t2, ..., tN) as follows:
+// 1. (t1.*f)(t2, ..., tN) when f is a pointer to a member function of a class T
+// and t1 is an object of type T or a reference to an object of type T or a
+// reference to an object of a type derived from T;
+// 2. ((*t1).*f)(t2, ..., tN) when f is a pointer to a member function of a
+// class T and t1 is not one of the types described in the previous item;
+// 3. t1.*f when N == 1 and f is a pointer to member data of a class T and t1 is
+// an object of type T or a reference to an object of type T or a reference
+// to an object of a type derived from T;
+// 4. (*t1).*f when N == 1 and f is a pointer to member data of a class T and t1
+// is not one of the types described in the previous item;
+// 5. f(t1, t2, ..., tN) in all other cases.
+//
+// The implementation is SFINAE-friendly: substitution failure within Invoke()
+// isn't an error.
+
+#ifndef ABSL_BASE_INTERNAL_INVOKE_H_
+#define ABSL_BASE_INTERNAL_INVOKE_H_
+
+#include <algorithm>
+#include <type_traits>
+#include <utility>
+
+// The following code is internal implementation detail. See the comment at the
+// top of this file for the API documentation.
+
+namespace absl {
+namespace base_internal {
+
+// The five classes below each implement one of the clauses from the definition
+// of INVOKE. The inner class template Accept<F, Args...> checks whether the
+// clause is applicable; static function template Invoke(f, args...) does the
+// invocation.
+//
+// By separating the clause selection logic from invocation we make sure that
+// Invoke() does exactly what the standard says.
+
+template <typename Derived>
+struct StrippedAccept {
+ template <typename... Args>
+ struct Accept : Derived::template AcceptImpl<typename std::remove_cv<
+ typename std::remove_reference<Args>::type>::type...> {};
+};
+
+// (t1.*f)(t2, ..., tN) when f is a pointer to a member function of a class T
+// and t1 is an object of type T or a reference to an object of type T or a
+// reference to an object of a type derived from T.
+struct MemFunAndRef : StrippedAccept<MemFunAndRef> {
+ template <typename... Args>
+ struct AcceptImpl : std::false_type {};
+
+ template <typename R, typename C, typename... Params, typename Obj,
+ typename... Args>
+ struct AcceptImpl<R (C::*)(Params...), Obj, Args...>
+ : std::is_base_of<C, Obj> {};
+
+ template <typename R, typename C, typename... Params, typename Obj,
+ typename... Args>
+ struct AcceptImpl<R (C::*)(Params...) const, Obj, Args...>
+ : std::is_base_of<C, Obj> {};
+
+ template <typename MemFun, typename Obj, typename... Args>
+ static decltype((std::declval<Obj>().*
+ std::declval<MemFun>())(std::declval<Args>()...))
+ Invoke(MemFun&& mem_fun, Obj&& obj, Args&&... args) {
+ return (std::forward<Obj>(obj).*
+ std::forward<MemFun>(mem_fun))(std::forward<Args>(args)...);
+ }
+};
+
+// ((*t1).*f)(t2, ..., tN) when f is a pointer to a member function of a
+// class T and t1 is not one of the types described in the previous item.
+struct MemFunAndPtr : StrippedAccept<MemFunAndPtr> {
+ template <typename... Args>
+ struct AcceptImpl : std::false_type {};
+
+ template <typename R, typename C, typename... Params, typename Ptr,
+ typename... Args>
+ struct AcceptImpl<R (C::*)(Params...), Ptr, Args...>
+ : std::integral_constant<bool, !std::is_base_of<C, Ptr>::value> {};
+
+ template <typename R, typename C, typename... Params, typename Ptr,
+ typename... Args>
+ struct AcceptImpl<R (C::*)(Params...) const, Ptr, Args...>
+ : std::integral_constant<bool, !std::is_base_of<C, Ptr>::value> {};
+
+ template <typename MemFun, typename Ptr, typename... Args>
+ static decltype(((*std::declval<Ptr>()).*
+ std::declval<MemFun>())(std::declval<Args>()...))
+ Invoke(MemFun&& mem_fun, Ptr&& ptr, Args&&... args) {
+ return ((*std::forward<Ptr>(ptr)).*
+ std::forward<MemFun>(mem_fun))(std::forward<Args>(args)...);
+ }
+};
+
+// t1.*f when N == 1 and f is a pointer to member data of a class T and t1 is
+// an object of type T or a reference to an object of type T or a reference
+// to an object of a type derived from T.
+struct DataMemAndRef : StrippedAccept<DataMemAndRef> {
+ template <typename... Args>
+ struct AcceptImpl : std::false_type {};
+
+ template <typename R, typename C, typename Obj>
+ struct AcceptImpl<R C::*, Obj> : std::is_base_of<C, Obj> {};
+
+ template <typename DataMem, typename Ref>
+ static decltype(std::declval<Ref>().*std::declval<DataMem>()) Invoke(
+ DataMem&& data_mem, Ref&& ref) {
+ return std::forward<Ref>(ref).*std::forward<DataMem>(data_mem);
+ }
+};
+
+// (*t1).*f when N == 1 and f is a pointer to member data of a class T and t1
+// is not one of the types described in the previous item.
+struct DataMemAndPtr : StrippedAccept<DataMemAndPtr> {
+ template <typename... Args>
+ struct AcceptImpl : std::false_type {};
+
+ template <typename R, typename C, typename Ptr>
+ struct AcceptImpl<R C::*, Ptr>
+ : std::integral_constant<bool, !std::is_base_of<C, Ptr>::value> {};
+
+ template <typename DataMem, typename Ptr>
+ static decltype((*std::declval<Ptr>()).*std::declval<DataMem>()) Invoke(
+ DataMem&& data_mem, Ptr&& ptr) {
+ return (*std::forward<Ptr>(ptr)).*std::forward<DataMem>(data_mem);
+ }
+};
+
+// f(t1, t2, ..., tN) in all other cases.
+struct Callable {
+ // Callable doesn't have Accept because it's the last clause that gets picked
+ // when none of the previous clauses are applicable.
+ template <typename F, typename... Args>
+ static decltype(std::declval<F>()(std::declval<Args>()...)) Invoke(
+ F&& f, Args&&... args) {
+ return std::forward<F>(f)(std::forward<Args>(args)...);
+ }
+};
+
+// Resolves to the first matching clause.
+template <typename... Args>
+struct Invoker {
+ typedef typename std::conditional<
+ MemFunAndRef::Accept<Args...>::value, MemFunAndRef,
+ typename std::conditional<
+ MemFunAndPtr::Accept<Args...>::value, MemFunAndPtr,
+ typename std::conditional<
+ DataMemAndRef::Accept<Args...>::value, DataMemAndRef,
+ typename std::conditional<DataMemAndPtr::Accept<Args...>::value,
+ DataMemAndPtr, Callable>::type>::type>::
+ type>::type type;
+};
+
+// The result type of Invoke<F, Args...>.
+template <typename F, typename... Args>
+using InvokeT = decltype(Invoker<F, Args...>::type::Invoke(
+ std::declval<F>(), std::declval<Args>()...));
+
+// Invoke(f, args...) is an implementation of INVOKE(f, args...) from section
+// [func.require] of the C++ standard.
+template <typename F, typename... Args>
+InvokeT<F, Args...> Invoke(F&& f, Args&&... args) {
+ return Invoker<F, Args...>::type::Invoke(std::forward<F>(f),
+ std::forward<Args>(args)...);
+}
+} // namespace base_internal
+} // namespace absl
+
+#endif // ABSL_BASE_INTERNAL_INVOKE_H_
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