EIC code displayed by LXR master/​include/​absl/​flags/​commandlineflag.h	Source navigation Diff markup Identifier search General search
	Version: master test Revert   Change

File indexing completed on 2025-01-18 09:27:16

 //
 // Copyright 2020 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: commandlineflag.h
 // -----------------------------------------------------------------------------
 //
 // This header file defines the `CommandLineFlag`, which acts as a type-erased
 // handle for accessing metadata about the Abseil Flag in question.
 //
 // Because an actual Abseil flag is of an unspecified type, you should not
 // manipulate or interact directly with objects of that type. Instead, use the
 // CommandLineFlag type as an intermediary.
 #ifndef ABSL_FLAGS_COMMANDLINEFLAG_H_
 #define ABSL_FLAGS_COMMANDLINEFLAG_H_
 
 #include <memory>
 #include <string>
 
 #include "absl/base/config.h"
 #include "absl/base/internal/fast_type_id.h"
 #include "absl/flags/internal/commandlineflag.h"
 #include "absl/strings/string_view.h"
 #include "absl/types/optional.h"
 
 namespace absl {
 ABSL_NAMESPACE_BEGIN
 namespace flags_internal {
 class PrivateHandleAccessor;
 }  // namespace flags_internal
 
 // CommandLineFlag
 //
 // This type acts as a type-erased handle for an instance of an Abseil Flag and
 // holds reflection information pertaining to that flag. Use CommandLineFlag to
 // access a flag's name, location, help string etc.
 //
 // To obtain an absl::CommandLineFlag, invoke `absl::FindCommandLineFlag()`
 // passing it the flag name string.
 //
 // Example:
 //
 //   // Obtain reflection handle for a flag named "flagname".
 //   const absl::CommandLineFlag* my_flag_data =
 //        absl::FindCommandLineFlag("flagname");
 //
 //   // Now you can get flag info from that reflection handle.
 //   std::string flag_location = my_flag_data->Filename();
 //   ...
 
 // These are only used as constexpr global objects.
 // They do not use a virtual destructor to simplify their implementation.
 // They are not destroyed except at program exit, so leaks do not matter.
 #if defined(__GNUC__) && !defined(__clang__)
 #pragma GCC diagnostic push
 #pragma GCC diagnostic ignored "-Wnon-virtual-dtor"
 #endif
 class CommandLineFlag {
  public:
   constexpr CommandLineFlag() = default;
 
   // Not copyable/assignable.
   CommandLineFlag(const CommandLineFlag&) = delete;
   CommandLineFlag& operator=(const CommandLineFlag&) = delete;
 
   // absl::CommandLineFlag::IsOfType()
   //
   // Return true iff flag has type T.
   template <typename T>
   inline bool IsOfType() const {
     return TypeId() == base_internal::FastTypeId<T>();
   }
 
   // absl::CommandLineFlag::TryGet()
   //
   // Attempts to retrieve the flag value. Returns value on success,
   // absl::nullopt otherwise.
   template <typename T>
   absl::optional<T> TryGet() const {
     if (IsRetired() || !IsOfType<T>()) {
       return absl::nullopt;
     }
 
     // Implementation notes:
     //
     // We are wrapping a union around the value of `T` to serve three purposes:
     //
     //  1. `U.value` has correct size and alignment for a value of type `T`
     //  2. The `U.value` constructor is not invoked since U's constructor does
     //     not do it explicitly.
     //  3. The `U.value` destructor is invoked since U's destructor does it
     //     explicitly. This makes `U` a kind of RAII wrapper around non default
     //     constructible value of T, which is destructed when we leave the
     //     scope. We do need to destroy U.value, which is constructed by
     //     CommandLineFlag::Read even though we left it in a moved-from state
     //     after std::move.
     //
     // All of this serves to avoid requiring `T` being default constructible.
     union U {
       T value;
       U() {}
       ~U() { value.~T(); }
     };
     U u;
 
     Read(&u.value);
     // allow retired flags to be "read", so we can report invalid access.
     if (IsRetired()) {
       return absl::nullopt;
     }
     return std::move(u.value);
   }
 
   // absl::CommandLineFlag::Name()
   //
   // Returns name of this flag.
   virtual absl::string_view Name() const = 0;
 
   // absl::CommandLineFlag::Filename()
   //
   // Returns name of the file where this flag is defined.
   virtual std::string Filename() const = 0;
 
   // absl::CommandLineFlag::Help()
   //
   // Returns help message associated with this flag.
   virtual std::string Help() const = 0;
 
   // absl::CommandLineFlag::IsRetired()
   //
   // Returns true iff this object corresponds to retired flag.
   virtual bool IsRetired() const;
 
   // absl::CommandLineFlag::DefaultValue()
   //
   // Returns the default value for this flag.
   virtual std::string DefaultValue() const = 0;
 
   // absl::CommandLineFlag::CurrentValue()
   //
   // Returns the current value for this flag.
   virtual std::string CurrentValue() const = 0;
 
   // absl::CommandLineFlag::ParseFrom()
   //
   // Sets the value of the flag based on specified string `value`. If the flag
   // was successfully set to new value, it returns true. Otherwise, sets `error`
   // to indicate the error, leaves the flag unchanged, and returns false.
   bool ParseFrom(absl::string_view value, std::string* error);
 
  protected:
   ~CommandLineFlag() = default;
 
  private:
   friend class flags_internal::PrivateHandleAccessor;
 
   // Sets the value of the flag based on specified string `value`. If the flag
   // was successfully set to new value, it returns true. Otherwise, sets `error`
   // to indicate the error, leaves the flag unchanged, and returns false. There
   // are three ways to set the flag's value:
   //  * Update the current flag value
   //  * Update the flag's default value
   //  * Update the current flag value if it was never set before
   // The mode is selected based on `set_mode` parameter.
   virtual bool ParseFrom(absl::string_view value,
                          flags_internal::FlagSettingMode set_mode,
                          flags_internal::ValueSource source,
                          std::string& error) = 0;
 
   // Returns id of the flag's value type.
   virtual flags_internal::FlagFastTypeId TypeId() const = 0;
 
   // Interface to save flag to some persistent state. Returns current flag state
   // or nullptr if flag does not support saving and restoring a state.
   virtual std::unique_ptr<flags_internal::FlagStateInterface> SaveState() = 0;
 
   // Copy-construct a new value of the flag's type in a memory referenced by
   // the dst based on the current flag's value.
   virtual void Read(void* dst) const = 0;
 
   // To be deleted. Used to return true if flag's current value originated from
   // command line.
   virtual bool IsSpecifiedOnCommandLine() const = 0;
 
   // Validates supplied value using validator or parseflag routine
   virtual bool ValidateInputValue(absl::string_view value) const = 0;
 
   // Checks that flags default value can be converted to string and back to the
   // flag's value type.
   virtual void CheckDefaultValueParsingRoundtrip() const = 0;
 };
 #if defined(__GNUC__) && !defined(__clang__)
 #pragma GCC diagnostic pop
 #endif
 
 ABSL_NAMESPACE_END
 }  // namespace absl
 
 #endif  // ABSL_FLAGS_COMMANDLINEFLAG_H_

This page was automatically generated by the 2.3.7 LXR engine. The LXR team