Export of internal Abseil changes
-- 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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Abseil Team
CJ Johnson
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commit
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31 changed files with 1972 additions and 1421 deletions
152
absl/functional/bind_front.h
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152
absl/functional/bind_front.h
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// Copyright 2018 The Abseil Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// https://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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// `absl::bind_front()` returns a functor by binding a number of arguments to
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// the front of a provided functor, allowing you to avoid known problems with
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// `std::bind()`. It is a form of partial function application
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// https://en.wikipedia.org/wiki/Partial_application.
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//
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// Like `std::bind()` it is implicitly convertible to `std::function`. In
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// particular, it may be used as a simpler replacement for `std::bind()` in most
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// cases, as it does not require placeholders to be specified. More
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// importantly, it provides more reliable correctness guarantees than
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// `std::bind()`.
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//
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// absl::bind_front(a...) can be seen as storing the results of
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// std::make_tuple(a...).
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//
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// Example: Binding a free function.
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//
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// int Minus(int a, int b) { return a - b; }
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//
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// assert(absl::bind_front(Minus)(3, 2) == 3 - 2);
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// assert(absl::bind_front(Minus, 3)(2) == 3 - 2);
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// assert(absl::bind_front(Minus, 3, 2)() == 3 - 2);
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//
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// Example: Binding a member function.
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//
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// struct Math {
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// int Double(int a) const { return 2 * a; }
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// };
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//
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// Math math;
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//
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// assert(absl::bind_front(&Math::Double)(&math, 3) == 2 * 3);
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// // Stores a pointer to math inside the functor.
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// assert(absl::bind_front(&Math::Double, &math)(3) == 2 * 3);
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// // Stores a copy of math inside the functor.
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// assert(absl::bind_front(&Math::Double, math)(3) == 2 * 3);
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// // Stores std::unique_ptr<Math> inside the functor.
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// assert(absl::bind_front(&Math::Double,
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// std::unique_ptr<Math>(new Math))(3) == 2 * 3);
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//
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// Example: Using `absl::bind_front()`, instead of `std::bind()`, with
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// `std::function`.
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//
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// class FileReader {
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// public:
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// void ReadFileAsync(const std::string& filename, std::string* content,
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// const std::function<void()>& done) {
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// // Calls Executor::Schedule(std::function<void()>).
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// Executor::DefaultExecutor()->Schedule(
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// absl::bind_front(&FileReader::BlockingRead, this,
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// filename, content, done));
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// }
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//
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// private:
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// void BlockingRead(const std::string& filename, std::string* content,
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// const std::function<void()>& done) {
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// CHECK_OK(file::GetContents(filename, content, {}));
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// done();
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// }
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// };
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//
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// `absl::bind_front()` stores bound arguments explicitly using the type passed
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// rather than implicitly based on the type accepted by its functor.
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//
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// Example: Binding arguments explicitly.
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//
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// void LogStringView(absl::string_view sv) {
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// LOG(INFO) << sv;
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// }
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//
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// Executor* e = Executor::DefaultExecutor();
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// std::string s = "hello";
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// absl::string_view sv = s;
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//
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// // absl::bind_front(LogStringView, arg) makes a copy of arg and stores it.
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// e->Schedule(absl::bind_front(LogStringView, sv)); // ERROR: dangling
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// // string_view.
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//
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// e->Schedule(absl::bind_front(LogStringView, s)); // OK: stores a copy of
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// // s.
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//
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// To store some of the arguments passed to `absl::bind_front()` by reference,
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// use std::ref()` and `std::cref()`.
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//
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// Example: Storing some of the bound arguments by reference.
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//
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// class Service {
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// public:
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// void Serve(const Request& req, std::function<void()>* done) {
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// // The request protocol buffer won't be deleted until done is called.
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// // It's safe to store a reference to it inside the functor.
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// Executor::DefaultExecutor()->Schedule(
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// absl::bind_front(&Service::BlockingServe, this, std::cref(req),
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// done));
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// }
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//
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// private:
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// void BlockingServe(const Request& req, std::function<void()>* done);
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// };
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//
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// Example: Storing bound arguments by reference.
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//
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// void Print(const string& a, const string& b) { LOG(INFO) << a << b; }
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//
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// std::string hi = "Hello, ";
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// std::vector<std::string> names = {"Chuk", "Gek"};
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// // Doesn't copy hi.
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// for_each(names.begin(), names.end(),
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// absl::bind_front(Print, std::ref(hi)));
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//
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// // DO NOT DO THIS: the functor may outlive "hi", resulting in
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// // dangling references.
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// foo->DoInFuture(absl::bind_front(Print, std::ref(hi), "Guest")); // BAD!
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// auto f = absl::bind_front(Print, std::ref(hi), "Guest"); // BAD!
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#ifndef ABSL_FUNCTIONAL_BIND_FRONT_H_
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#define ABSL_FUNCTIONAL_BIND_FRONT_H_
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#include "absl/functional/internal/front_binder.h"
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#include "absl/utility/utility.h"
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namespace absl {
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ABSL_NAMESPACE_BEGIN
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// Binds the first N arguments of an invocable object and stores them by value,
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// except types of std::reference_wrapper which are 'unwound' and stored by
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// reference.
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template <class F, class... BoundArgs>
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constexpr functional_internal::bind_front_t<F, BoundArgs...> bind_front(
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F&& func, BoundArgs&&... args) {
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return functional_internal::bind_front_t<F, BoundArgs...>(
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absl::in_place, absl::forward<F>(func),
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absl::forward<BoundArgs>(args)...);
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}
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ABSL_NAMESPACE_END
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} // namespace absl
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#endif // ABSL_FUNCTIONAL_BIND_FRONT_H_
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