diff options
Diffstat (limited to 'abseil-cpp/absl/cleanup/cleanup.h')
-rw-r--r-- | abseil-cpp/absl/cleanup/cleanup.h | 140 |
1 files changed, 140 insertions, 0 deletions
diff --git a/abseil-cpp/absl/cleanup/cleanup.h b/abseil-cpp/absl/cleanup/cleanup.h new file mode 100644 index 0000000..960ccd0 --- /dev/null +++ b/abseil-cpp/absl/cleanup/cleanup.h @@ -0,0 +1,140 @@ +// Copyright 2021 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. +// +// ----------------------------------------------------------------------------- +// File: cleanup.h +// ----------------------------------------------------------------------------- +// +// `absl::Cleanup` implements the scope guard idiom, invoking the contained +// callback's `operator()() &&` on scope exit. +// +// Example: +// +// ``` +// absl::Status CopyGoodData(const char* source_path, const char* sink_path) { +// FILE* source_file = fopen(source_path, "r"); +// if (source_file == nullptr) { +// return absl::NotFoundError("No source file"); // No cleanups execute +// } +// +// // C++17 style cleanup using class template argument deduction +// absl::Cleanup source_closer = [source_file] { fclose(source_file); }; +// +// FILE* sink_file = fopen(sink_path, "w"); +// if (sink_file == nullptr) { +// return absl::NotFoundError("No sink file"); // First cleanup executes +// } +// +// // C++11 style cleanup using the factory function +// auto sink_closer = absl::MakeCleanup([sink_file] { fclose(sink_file); }); +// +// Data data; +// while (ReadData(source_file, &data)) { +// if (!data.IsGood()) { +// absl::Status result = absl::FailedPreconditionError("Read bad data"); +// return result; // Both cleanups execute +// } +// SaveData(sink_file, &data); +// } +// +// return absl::OkStatus(); // Both cleanups execute +// } +// ``` +// +// Methods: +// +// `std::move(cleanup).Cancel()` will prevent the callback from executing. +// +// `std::move(cleanup).Invoke()` will execute the callback early, before +// destruction, and prevent the callback from executing in the destructor. +// +// Usage: +// +// `absl::Cleanup` is not an interface type. It is only intended to be used +// within the body of a function. It is not a value type and instead models a +// control flow construct. Check out `defer` in Golang for something similar. + +#ifndef ABSL_CLEANUP_CLEANUP_H_ +#define ABSL_CLEANUP_CLEANUP_H_ + +#include <utility> + +#include "absl/base/config.h" +#include "absl/base/macros.h" +#include "absl/cleanup/internal/cleanup.h" + +namespace absl { +ABSL_NAMESPACE_BEGIN + +template <typename Arg, typename Callback = void()> +class ABSL_MUST_USE_RESULT Cleanup final { + static_assert(cleanup_internal::WasDeduced<Arg>(), + "Explicit template parameters are not supported."); + + static_assert(cleanup_internal::ReturnsVoid<Callback>(), + "Callbacks that return values are not supported."); + + public: + Cleanup(Callback callback) : storage_(std::move(callback)) {} // NOLINT + + Cleanup(Cleanup&& other) = default; + + void Cancel() && { + ABSL_HARDENING_ASSERT(storage_.IsCallbackEngaged()); + storage_.DestroyCallback(); + } + + void Invoke() && { + ABSL_HARDENING_ASSERT(storage_.IsCallbackEngaged()); + storage_.InvokeCallback(); + storage_.DestroyCallback(); + } + + ~Cleanup() { + if (storage_.IsCallbackEngaged()) { + storage_.InvokeCallback(); + storage_.DestroyCallback(); + } + } + + private: + cleanup_internal::Storage<Callback> storage_; +}; + +// `absl::Cleanup c = /* callback */;` +// +// C++17 type deduction API for creating an instance of `absl::Cleanup` +#if defined(ABSL_HAVE_CLASS_TEMPLATE_ARGUMENT_DEDUCTION) +template <typename Callback> +Cleanup(Callback callback) -> Cleanup<cleanup_internal::Tag, Callback>; +#endif // defined(ABSL_HAVE_CLASS_TEMPLATE_ARGUMENT_DEDUCTION) + +// `auto c = absl::MakeCleanup(/* callback */);` +// +// C++11 type deduction API for creating an instance of `absl::Cleanup` +template <typename... Args, typename Callback> +absl::Cleanup<cleanup_internal::Tag, Callback> MakeCleanup(Callback callback) { + static_assert(cleanup_internal::WasDeduced<cleanup_internal::Tag, Args...>(), + "Explicit template parameters are not supported."); + + static_assert(cleanup_internal::ReturnsVoid<Callback>(), + "Callbacks that return values are not supported."); + + return {std::move(callback)}; +} + +ABSL_NAMESPACE_END +} // namespace absl + +#endif // ABSL_CLEANUP_CLEANUP_H_ |