absl/flags/reflection.h

0001 //
0002 // Copyright 2020 The Abseil Authors.
0003 //
0004 // Licensed under the Apache License, Version 2.0 (the "License");
0005 // you may not use this file except in compliance with the License.
0006 // You may obtain a copy of the License at
0007 //
0008 //      https://www.apache.org/licenses/LICENSE-2.0
0009 //
0010 // Unless required by applicable law or agreed to in writing, software
0011 // distributed under the License is distributed on an "AS IS" BASIS,
0012 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
0013 // See the License for the specific language governing permissions and
0014 // limitations under the License.
0015 //
0016 // -----------------------------------------------------------------------------
0017 // File: reflection.h
0018 // -----------------------------------------------------------------------------
0019 //
0020 // This file defines the routines to access and operate on an Abseil Flag's
0021 // reflection handle.
0022
0023 #ifndef ABSL_FLAGS_REFLECTION_H_
0024 #define ABSL_FLAGS_REFLECTION_H_
0025
0026 #include <string>
0027
0028 #include "absl/base/config.h"
0029 #include "absl/container/flat_hash_map.h"
0030 #include "absl/flags/commandlineflag.h"
0031 #include "absl/flags/internal/commandlineflag.h"
0032
0033 namespace absl {
0034 ABSL_NAMESPACE_BEGIN
0035 namespace flags_internal {
0036 class FlagSaverImpl;
0037 }  // namespace flags_internal
0038
0039 // FindCommandLineFlag()
0040 //
0041 // Returns the reflection handle of an Abseil flag of the specified name, or
0042 // `nullptr` if not found. This function will emit a warning if the name of a
0043 // 'retired' flag is specified.
0044 absl::CommandLineFlag* FindCommandLineFlag(absl::string_view name);
0045
0046 // Returns current state of the Flags registry in a form of mapping from flag
0047 // name to a flag reflection handle.
0048 absl::flat_hash_map<absl::string_view, absl::CommandLineFlag*> GetAllFlags();
0049
0050 //------------------------------------------------------------------------------
0051 // FlagSaver
0052 //------------------------------------------------------------------------------
0053 //
0054 // A FlagSaver object stores the state of flags in the scope where the FlagSaver
0055 // is defined, allowing modification of those flags within that scope and
0056 // automatic restoration of the flags to their previous state upon leaving the
0057 // scope.
0058 //
0059 // A FlagSaver can be used within tests to temporarily change the test
0060 // environment and restore the test case to its previous state.
0061 //
0062 // Example:
0063 //
0064 //   void MyFunc() {
0065 //    absl::FlagSaver fs;
0066 //    ...
0067 //    absl::SetFlag(&FLAGS_myFlag, otherValue);
0068 //    ...
0069 //  } // scope of FlagSaver left, flags return to previous state
0070 //
0071 // This class is thread-safe.
0072
0073 class FlagSaver {
0074  public:
0075   FlagSaver();
0076   ~FlagSaver();
0077
0078   FlagSaver(const FlagSaver&) = delete;
0079   void operator=(const FlagSaver&) = delete;
0080
0081  private:
0082   flags_internal::FlagSaverImpl* impl_;
0083 };
0084
0085 //-----------------------------------------------------------------------------
0086
0087 ABSL_NAMESPACE_END
0088 }  // namespace absl
0089
0090 #endif  // ABSL_FLAGS_REFLECTION_H_