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-- 20b3acaff75d05315f272747956b01405adccafb by Greg Falcon <gfalcon@google.com>: Re-import of CCTZ from GitHub, with new ABSL_NAMESPACE_ transform applied. PiperOrigin-RevId: 285564474 -- 4d9e3fcabcea33c8b0b69f094ad2eddc0fa19557 by Derek Mauro <dmauro@google.com>: Moves the disabling of a warning to before the function begins. MSVC apparently requires this for warnings in the range 4700-4999. https://docs.microsoft.com/en-us/cpp/preprocessor/warning?redirectedfrom=MSDN&view=vs-2019 PiperOrigin-RevId: 285516232 -- 4a060cbeda76e89693c50276ae5b62cbf0fff39a by Derek Mauro <dmauro@google.com>: MSVC: Fixes uniform_real_distribution_test in opt mode Disables a constant arithmetic overflow warning in a test that tests the behavior on overflow. This should be tested because a user might have this warning disabled. PiperOrigin-RevId: 285452242 -- 548ab2f4cbe59bd6f6bf493af4f9ea765c4fa949 by Andy Soffer <asoffer@google.com>: Release absl::bind_front, a C++11-compliant work-alike type for the C++20 std::bind_front. PiperOrigin-RevId: 285247872 GitOrigin-RevId: 20b3acaff75d05315f272747956b01405adccafb Change-Id: I00fe45939246cba9bfc7be375d67787d2eb57cd3
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// Copyright 2018 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. | ||
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// `absl::bind_front()` returns a functor by binding a number of arguments to | ||
// the front of a provided functor, allowing you to avoid known problems with | ||
// `std::bind()`. It is a form of partial function application | ||
// https://en.wikipedia.org/wiki/Partial_application. | ||
// | ||
// Like `std::bind()` it is implicitly convertible to `std::function`. In | ||
// particular, it may be used as a simpler replacement for `std::bind()` in most | ||
// cases, as it does not require placeholders to be specified. More | ||
// importantly, it provides more reliable correctness guarantees than | ||
// `std::bind()`. | ||
// | ||
// absl::bind_front(a...) can be seen as storing the results of | ||
// std::make_tuple(a...). | ||
// | ||
// Example: Binding a free function. | ||
// | ||
// int Minus(int a, int b) { return a - b; } | ||
// | ||
// assert(absl::bind_front(Minus)(3, 2) == 3 - 2); | ||
// assert(absl::bind_front(Minus, 3)(2) == 3 - 2); | ||
// assert(absl::bind_front(Minus, 3, 2)() == 3 - 2); | ||
// | ||
// Example: Binding a member function. | ||
// | ||
// struct Math { | ||
// int Double(int a) const { return 2 * a; } | ||
// }; | ||
// | ||
// Math math; | ||
// | ||
// assert(absl::bind_front(&Math::Double)(&math, 3) == 2 * 3); | ||
// // Stores a pointer to math inside the functor. | ||
// assert(absl::bind_front(&Math::Double, &math)(3) == 2 * 3); | ||
// // Stores a copy of math inside the functor. | ||
// assert(absl::bind_front(&Math::Double, math)(3) == 2 * 3); | ||
// // Stores std::unique_ptr<Math> inside the functor. | ||
// assert(absl::bind_front(&Math::Double, | ||
// std::unique_ptr<Math>(new Math))(3) == 2 * 3); | ||
// | ||
// Example: Using `absl::bind_front()`, instead of `std::bind()`, with | ||
// `std::function`. | ||
// | ||
// class FileReader { | ||
// public: | ||
// void ReadFileAsync(const std::string& filename, std::string* content, | ||
// const std::function<void()>& done) { | ||
// // Calls Executor::Schedule(std::function<void()>). | ||
// Executor::DefaultExecutor()->Schedule( | ||
// absl::bind_front(&FileReader::BlockingRead, this, | ||
// filename, content, done)); | ||
// } | ||
// | ||
// private: | ||
// void BlockingRead(const std::string& filename, std::string* content, | ||
// const std::function<void()>& done) { | ||
// CHECK_OK(file::GetContents(filename, content, {})); | ||
// done(); | ||
// } | ||
// }; | ||
// | ||
// `absl::bind_front()` stores bound arguments explicitly using the type passed | ||
// rather than implicitly based on the type accepted by its functor. | ||
// | ||
// Example: Binding arguments explicitly. | ||
// | ||
// void LogStringView(absl::string_view sv) { | ||
// LOG(INFO) << sv; | ||
// } | ||
// | ||
// Executor* e = Executor::DefaultExecutor(); | ||
// std::string s = "hello"; | ||
// absl::string_view sv = s; | ||
// | ||
// // absl::bind_front(LogStringView, arg) makes a copy of arg and stores it. | ||
// e->Schedule(absl::bind_front(LogStringView, sv)); // ERROR: dangling | ||
// // string_view. | ||
// | ||
// e->Schedule(absl::bind_front(LogStringView, s)); // OK: stores a copy of | ||
// // s. | ||
// | ||
// To store some of the arguments passed to `absl::bind_front()` by reference, | ||
// use std::ref()` and `std::cref()`. | ||
// | ||
// Example: Storing some of the bound arguments by reference. | ||
// | ||
// class Service { | ||
// public: | ||
// void Serve(const Request& req, std::function<void()>* done) { | ||
// // The request protocol buffer won't be deleted until done is called. | ||
// // It's safe to store a reference to it inside the functor. | ||
// Executor::DefaultExecutor()->Schedule( | ||
// absl::bind_front(&Service::BlockingServe, this, std::cref(req), | ||
// done)); | ||
// } | ||
// | ||
// private: | ||
// void BlockingServe(const Request& req, std::function<void()>* done); | ||
// }; | ||
// | ||
// Example: Storing bound arguments by reference. | ||
// | ||
// void Print(const string& a, const string& b) { LOG(INFO) << a << b; } | ||
// | ||
// std::string hi = "Hello, "; | ||
// std::vector<std::string> names = {"Chuk", "Gek"}; | ||
// // Doesn't copy hi. | ||
// for_each(names.begin(), names.end(), | ||
// absl::bind_front(Print, std::ref(hi))); | ||
// | ||
// // DO NOT DO THIS: the functor may outlive "hi", resulting in | ||
// // dangling references. | ||
// foo->DoInFuture(absl::bind_front(Print, std::ref(hi), "Guest")); // BAD! | ||
// auto f = absl::bind_front(Print, std::ref(hi), "Guest"); // BAD! | ||
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#ifndef ABSL_FUNCTIONAL_BIND_FRONT_H_ | ||
#define ABSL_FUNCTIONAL_BIND_FRONT_H_ | ||
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#include "absl/functional/internal/front_binder.h" | ||
#include "absl/utility/utility.h" | ||
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namespace absl { | ||
ABSL_NAMESPACE_BEGIN | ||
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// Binds the first N arguments of an invocable object and stores them by value, | ||
// except types of std::reference_wrapper which are 'unwound' and stored by | ||
// reference. | ||
template <class F, class... BoundArgs> | ||
constexpr functional_internal::bind_front_t<F, BoundArgs...> bind_front( | ||
F&& func, BoundArgs&&... args) { | ||
return functional_internal::bind_front_t<F, BoundArgs...>( | ||
absl::in_place, absl::forward<F>(func), | ||
absl::forward<BoundArgs>(args)...); | ||
} | ||
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ABSL_NAMESPACE_END | ||
} // namespace absl | ||
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#endif // ABSL_FUNCTIONAL_BIND_FRONT_H_ |
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