EIC code displayed by LXR |
|
|
|
|||
File indexing completed on 2024-11-15 09:01:03
0001 // Copyright 2018 The Abseil Authors. 0002 // 0003 // Licensed under the Apache License, Version 2.0 (the "License"); 0004 // you may not use this file except in compliance with the License. 0005 // You may obtain a copy of the License at 0006 // 0007 // https://www.apache.org/licenses/LICENSE-2.0 0008 // 0009 // Unless required by applicable law or agreed to in writing, software 0010 // distributed under the License is distributed on an "AS IS" BASIS, 0011 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 0012 // See the License for the specific language governing permissions and 0013 // limitations under the License. 0014 // 0015 // ----------------------------------------------------------------------------- 0016 // File: bind_front.h 0017 // ----------------------------------------------------------------------------- 0018 // 0019 // `absl::bind_front()` returns a functor by binding a number of arguments to 0020 // the front of a provided (usually more generic) functor. Unlike `std::bind`, 0021 // it does not require the use of argument placeholders. The simpler syntax of 0022 // `absl::bind_front()` allows you to avoid known misuses with `std::bind()`. 0023 // 0024 // `absl::bind_front()` is meant as a drop-in replacement for C++20's upcoming 0025 // `std::bind_front()`, which similarly resolves these issues with 0026 // `std::bind()`. Both `bind_front()` alternatives, unlike `std::bind()`, allow 0027 // partial function application. (See 0028 // https://en.wikipedia.org/wiki/Partial_application). 0029 0030 #ifndef ABSL_FUNCTIONAL_BIND_FRONT_H_ 0031 #define ABSL_FUNCTIONAL_BIND_FRONT_H_ 0032 0033 #if defined(__cpp_lib_bind_front) && __cpp_lib_bind_front >= 201907L 0034 #include <functional> // For std::bind_front. 0035 #endif // defined(__cpp_lib_bind_front) && __cpp_lib_bind_front >= 201907L 0036 0037 #include "absl/functional/internal/front_binder.h" 0038 #include "absl/utility/utility.h" 0039 0040 namespace absl { 0041 ABSL_NAMESPACE_BEGIN 0042 0043 // bind_front() 0044 // 0045 // Binds the first N arguments of an invocable object and stores them by value. 0046 // 0047 // Like `std::bind()`, `absl::bind_front()` is implicitly convertible to 0048 // `std::function`. In particular, it may be used as a simpler replacement for 0049 // `std::bind()` in most cases, as it does not require placeholders to be 0050 // specified. More importantly, it provides more reliable correctness guarantees 0051 // than `std::bind()`; while `std::bind()` will silently ignore passing more 0052 // parameters than expected, for example, `absl::bind_front()` will report such 0053 // mis-uses as errors. In C++20, `absl::bind_front` is replaced by 0054 // `std::bind_front`. 0055 // 0056 // absl::bind_front(a...) can be seen as storing the results of 0057 // std::make_tuple(a...). 0058 // 0059 // Example: Binding a free function. 0060 // 0061 // int Minus(int a, int b) { return a - b; } 0062 // 0063 // assert(absl::bind_front(Minus)(3, 2) == 3 - 2); 0064 // assert(absl::bind_front(Minus, 3)(2) == 3 - 2); 0065 // assert(absl::bind_front(Minus, 3, 2)() == 3 - 2); 0066 // 0067 // Example: Binding a member function. 0068 // 0069 // struct Math { 0070 // int Double(int a) const { return 2 * a; } 0071 // }; 0072 // 0073 // Math math; 0074 // 0075 // assert(absl::bind_front(&Math::Double)(&math, 3) == 2 * 3); 0076 // // Stores a pointer to math inside the functor. 0077 // assert(absl::bind_front(&Math::Double, &math)(3) == 2 * 3); 0078 // // Stores a copy of math inside the functor. 0079 // assert(absl::bind_front(&Math::Double, math)(3) == 2 * 3); 0080 // // Stores std::unique_ptr<Math> inside the functor. 0081 // assert(absl::bind_front(&Math::Double, 0082 // std::unique_ptr<Math>(new Math))(3) == 2 * 3); 0083 // 0084 // Example: Using `absl::bind_front()`, instead of `std::bind()`, with 0085 // `std::function`. 0086 // 0087 // class FileReader { 0088 // public: 0089 // void ReadFileAsync(const std::string& filename, std::string* content, 0090 // const std::function<void()>& done) { 0091 // // Calls Executor::Schedule(std::function<void()>). 0092 // Executor::DefaultExecutor()->Schedule( 0093 // absl::bind_front(&FileReader::BlockingRead, this, 0094 // filename, content, done)); 0095 // } 0096 // 0097 // private: 0098 // void BlockingRead(const std::string& filename, std::string* content, 0099 // const std::function<void()>& done) { 0100 // CHECK_OK(file::GetContents(filename, content, {})); 0101 // done(); 0102 // } 0103 // }; 0104 // 0105 // `absl::bind_front()` stores bound arguments explicitly using the type passed 0106 // rather than implicitly based on the type accepted by its functor. 0107 // 0108 // Example: Binding arguments explicitly. 0109 // 0110 // void LogStringView(absl::string_view sv) { 0111 // LOG(INFO) << sv; 0112 // } 0113 // 0114 // Executor* e = Executor::DefaultExecutor(); 0115 // std::string s = "hello"; 0116 // absl::string_view sv = s; 0117 // 0118 // // absl::bind_front(LogStringView, arg) makes a copy of arg and stores it. 0119 // e->Schedule(absl::bind_front(LogStringView, sv)); // ERROR: dangling 0120 // // string_view. 0121 // 0122 // e->Schedule(absl::bind_front(LogStringView, s)); // OK: stores a copy of 0123 // // s. 0124 // 0125 // To store some of the arguments passed to `absl::bind_front()` by reference, 0126 // use std::ref()` and `std::cref()`. 0127 // 0128 // Example: Storing some of the bound arguments by reference. 0129 // 0130 // class Service { 0131 // public: 0132 // void Serve(const Request& req, std::function<void()>* done) { 0133 // // The request protocol buffer won't be deleted until done is called. 0134 // // It's safe to store a reference to it inside the functor. 0135 // Executor::DefaultExecutor()->Schedule( 0136 // absl::bind_front(&Service::BlockingServe, this, std::cref(req), 0137 // done)); 0138 // } 0139 // 0140 // private: 0141 // void BlockingServe(const Request& req, std::function<void()>* done); 0142 // }; 0143 // 0144 // Example: Storing bound arguments by reference. 0145 // 0146 // void Print(const std::string& a, const std::string& b) { 0147 // std::cerr << a << b; 0148 // } 0149 // 0150 // std::string hi = "Hello, "; 0151 // std::vector<std::string> names = {"Chuk", "Gek"}; 0152 // // Doesn't copy hi. 0153 // for_each(names.begin(), names.end(), 0154 // absl::bind_front(Print, std::ref(hi))); 0155 // 0156 // // DO NOT DO THIS: the functor may outlive "hi", resulting in 0157 // // dangling references. 0158 // foo->DoInFuture(absl::bind_front(Print, std::ref(hi), "Guest")); // BAD! 0159 // auto f = absl::bind_front(Print, std::ref(hi), "Guest"); // BAD! 0160 // 0161 // Example: Storing reference-like types. 0162 // 0163 // void Print(absl::string_view a, const std::string& b) { 0164 // std::cerr << a << b; 0165 // } 0166 // 0167 // std::string hi = "Hello, "; 0168 // // Copies "hi". 0169 // absl::bind_front(Print, hi)("Chuk"); 0170 // 0171 // // Compile error: std::reference_wrapper<const string> is not implicitly 0172 // // convertible to string_view. 0173 // // absl::bind_front(Print, std::cref(hi))("Chuk"); 0174 // 0175 // // Doesn't copy "hi". 0176 // absl::bind_front(Print, absl::string_view(hi))("Chuk"); 0177 // 0178 #if defined(__cpp_lib_bind_front) && __cpp_lib_bind_front >= 201907L 0179 using std::bind_front; 0180 #else // defined(__cpp_lib_bind_front) && __cpp_lib_bind_front >= 201907L 0181 template <class F, class... BoundArgs> 0182 constexpr functional_internal::bind_front_t<F, BoundArgs...> bind_front( 0183 F&& func, BoundArgs&&... args) { 0184 return functional_internal::bind_front_t<F, BoundArgs...>( 0185 absl::in_place, absl::forward<F>(func), 0186 absl::forward<BoundArgs>(args)...); 0187 } 0188 #endif // defined(__cpp_lib_bind_front) && __cpp_lib_bind_front >= 201907L 0189 0190 ABSL_NAMESPACE_END 0191 } // namespace absl 0192 0193 #endif // ABSL_FUNCTIONAL_BIND_FRONT_H_
| [ Source navigation ] | [ Diff markup ] | [ Identifier search ] | [ general search ] |
|
This page was automatically generated by the 2.3.7 LXR engine. The LXR team |
|