function_ref.h (3990B)
1 // Copyright 2019 The Abseil Authors. 2 // 3 // Licensed under the Apache License, Version 2.0 (the "License"); 4 // you may not use this file except in compliance with the License. 5 // You may obtain a copy of the License at 6 // 7 // https://www.apache.org/licenses/LICENSE-2.0 8 // 9 // Unless required by applicable law or agreed to in writing, software 10 // distributed under the License is distributed on an "AS IS" BASIS, 11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12 // See the License for the specific language governing permissions and 13 // limitations under the License. 14 15 #ifndef ABSL_FUNCTIONAL_INTERNAL_FUNCTION_REF_H_ 16 #define ABSL_FUNCTIONAL_INTERNAL_FUNCTION_REF_H_ 17 18 #include <cassert> 19 #include <functional> 20 #include <type_traits> 21 22 #include "absl/functional/any_invocable.h" 23 #include "absl/meta/type_traits.h" 24 25 namespace absl { 26 ABSL_NAMESPACE_BEGIN 27 namespace functional_internal { 28 29 // Like a void* that can handle function pointers as well. The standard does not 30 // allow function pointers to round-trip through void*, but void(*)() is fine. 31 // 32 // Note: It's important that this class remains trivial and is the same size as 33 // a pointer, since this allows the compiler to perform tail-call optimizations 34 // when the underlying function is a callable object with a matching signature. 35 union VoidPtr { 36 const void* obj; 37 void (*fun)(); 38 }; 39 40 // Chooses the best type for passing T as an argument. 41 // Attempt to be close to SystemV AMD64 ABI. Objects with trivial copy ctor are 42 // passed by value. 43 template <typename T, 44 bool IsLValueReference = std::is_lvalue_reference<T>::value> 45 struct PassByValue : std::false_type {}; 46 47 template <typename T> 48 struct PassByValue<T, /*IsLValueReference=*/false> 49 : std::integral_constant<bool, 50 absl::is_trivially_copy_constructible<T>::value && 51 absl::is_trivially_copy_assignable< 52 typename std::remove_cv<T>::type>::value && 53 std::is_trivially_destructible<T>::value && 54 sizeof(T) <= 2 * sizeof(void*)> {}; 55 56 template <typename T> 57 struct ForwardT : std::conditional<PassByValue<T>::value, T, T&&> {}; 58 59 // An Invoker takes a pointer to the type-erased invokable object, followed by 60 // the arguments that the invokable object expects. 61 // 62 // Note: The order of arguments here is an optimization, since member functions 63 // have an implicit "this" pointer as their first argument, putting VoidPtr 64 // first allows the compiler to perform tail-call optimization in many cases. 65 template <typename R, typename... Args> 66 using Invoker = R (*)(VoidPtr, typename ForwardT<Args>::type...); 67 68 // 69 // InvokeObject and InvokeFunction provide static "Invoke" functions that can be 70 // used as Invokers for objects or functions respectively. 71 // 72 // static_cast<R> handles the case the return type is void. 73 template <typename Obj, typename R, typename... Args> 74 R InvokeObject(VoidPtr ptr, typename ForwardT<Args>::type... args) { 75 auto o = static_cast<const Obj*>(ptr.obj); 76 return static_cast<R>(std::invoke(*o, std::forward<Args>(args)...)); 77 } 78 79 template <typename Fun, typename R, typename... Args> 80 R InvokeFunction(VoidPtr ptr, typename ForwardT<Args>::type... args) { 81 auto f = reinterpret_cast<Fun>(ptr.fun); 82 return static_cast<R>(std::invoke(f, std::forward<Args>(args)...)); 83 } 84 85 template <typename Sig> 86 void AssertNonNull(const std::function<Sig>& f) { 87 assert(f != nullptr); 88 (void)f; 89 } 90 91 template <typename Sig> 92 void AssertNonNull(const AnyInvocable<Sig>& f) { 93 assert(f != nullptr); 94 (void)f; 95 } 96 97 template <typename F> 98 void AssertNonNull(const F&) {} 99 100 template <typename F, typename C> 101 void AssertNonNull(F C::*f) { 102 assert(f != nullptr); 103 (void)f; 104 } 105 106 template <bool C> 107 using EnableIf = typename ::std::enable_if<C, int>::type; 108 109 } // namespace functional_internal 110 ABSL_NAMESPACE_END 111 } // namespace absl 112 113 #endif // ABSL_FUNCTIONAL_INTERNAL_FUNCTION_REF_H_