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//
// Copyright 2019 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.
#ifndef ABSL_FLAGS_INTERNAL_COMMANDLINEFLAG_H_
#define ABSL_FLAGS_INTERNAL_COMMANDLINEFLAG_H_
#include <memory>
#include <string>
#include "absl/base/config.h"
#include "absl/base/internal/fast_type_id.h"
#include "absl/base/macros.h"
#include "absl/strings/string_view.h"
#include "absl/types/optional.h"
namespace absl {
ABSL_NAMESPACE_BEGIN
namespace flags_internal {
// An alias for flag fast type id. This value identifies the flag value type
// simialarly to typeid(T), without relying on RTTI being available. In most
// cases this id is enough to uniquely identify the flag's value type. In a few
// cases we'll have to resort to using actual RTTI implementation if it is
// available.
using FlagFastTypeId = base_internal::FastTypeIdType;
// Options that control SetCommandLineOptionWithMode.
enum FlagSettingMode {
// update the flag's value unconditionally (can call this multiple times).
SET_FLAGS_VALUE,
// update the flag's value, but *only if* it has not yet been updated
// with SET_FLAGS_VALUE, SET_FLAG_IF_DEFAULT, or "FLAGS_xxx = nondef".
SET_FLAG_IF_DEFAULT,
// set the flag's default value to this. If the flag has not been updated
// yet (via SET_FLAGS_VALUE, SET_FLAG_IF_DEFAULT, or "FLAGS_xxx = nondef")
// change the flag's current value to the new default value as well.
SET_FLAGS_DEFAULT
};
// Options that control ParseFrom: Source of a value.
enum ValueSource {
// Flag is being set by value specified on a command line.
kCommandLine,
// Flag is being set by value specified in the code.
kProgrammaticChange,
};
// Handle to FlagState objects. Specific flag state objects will restore state
// of a flag produced this flag state from method CommandLineFlag::SaveState().
class FlagStateInterface {
public:
virtual ~FlagStateInterface();
// Restores the flag originated this object to the saved state.
virtual void Restore() const = 0;
};
// Holds all information for a flag.
class CommandLineFlag {
public:
constexpr CommandLineFlag() = default;
// Not copyable/assignable.
CommandLineFlag(const CommandLineFlag&) = delete;
CommandLineFlag& operator=(const CommandLineFlag&) = delete;
// Non-polymorphic access methods.
// Return true iff flag has type T.
template <typename T>
inline bool IsOfType() const {
return TypeId() == base_internal::FastTypeId<T>();
}
// 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);
return std::move(u.value);
}
// Polymorphic access methods
// Returns name of this flag.
virtual absl::string_view Name() const = 0;
// Returns name of the file where this flag is defined.
virtual std::string Filename() const = 0;
// Returns help message associated with this flag.
virtual std::string Help() const = 0;
// Returns true iff this object corresponds to retired flag.
virtual bool IsRetired() const;
virtual std::string DefaultValue() const = 0;
virtual std::string CurrentValue() const = 0;
// 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 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 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<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 usign 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;
};
} // namespace flags_internal
ABSL_NAMESPACE_END
} // namespace absl
#endif // ABSL_FLAGS_INTERNAL_COMMANDLINEFLAG_H_
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