201 lines
6.9 KiB
C++
201 lines
6.9 KiB
C++
//
|
|
// 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();
|
|
// ...
|
|
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;
|
|
};
|
|
|
|
ABSL_NAMESPACE_END
|
|
} // namespace absl
|
|
|
|
#endif // ABSL_FLAGS_COMMANDLINEFLAG_H_
|