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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_FLAG_H_
#define ABSL_FLAGS_INTERNAL_FLAG_H_
#include "absl/flags/internal/commandlineflag.h"
#include "absl/flags/internal/registry.h"
namespace absl {
namespace flags_internal {
// This is "unspecified" implementation of absl::Flag<T> type.
template <typename T>
class Flag {
public:
constexpr Flag(const char* name, const flags_internal::HelpGenFunc help_gen,
const char* filename,
const flags_internal::FlagMarshallingOpFn marshalling_op,
const flags_internal::InitialValGenFunc initial_value_gen)
: internal(name, flags_internal::HelpText::FromFunctionPointer(help_gen),
filename, &flags_internal::FlagOps<T>, marshalling_op,
initial_value_gen,
/*retired_arg=*/false, /*def_arg=*/nullptr,
/*cur_arg=*/nullptr) {}
// Not copyable/assignable.
Flag(const Flag<T>&) = delete;
Flag<T>& operator=(const Flag<T>&) = delete;
absl::string_view Name() const { return internal.Name(); }
std::string Help() const { return internal.Help(); }
std::string Filename() const { return internal.Filename(); }
absl::flags_internal::CommandLineFlag internal;
void SetCallback(const flags_internal::FlagCallback mutation_callback) {
internal.SetCallback(mutation_callback);
}
private:
// TODO(rogeeff): add these validations once UnparseFlag invocation is fixed
// for built-in types and when we cleanup existing code from operating on
// forward declared types.
// auto IsCopyConstructible(const T& v) -> decltype(T(v));
// auto HasAbslParseFlag(absl::string_view in, T* dst, std::string* err)
// -> decltype(AbslParseFlag(in, dst, err));
// auto HasAbslUnparseFlag(const T& v) -> decltype(AbslUnparseFlag(v));
};
// This class facilitates Flag object registration and tail expression-based
// flag definition, for example:
// ABSL_FLAG(int, foo, 42, "Foo help").OnUpdate(NotifyFooWatcher);
template <typename T, bool do_register>
class FlagRegistrar {
public:
explicit FlagRegistrar(Flag<T>* flag) : flag_(flag) {
if (do_register) flags_internal::RegisterCommandLineFlag(&flag_->internal);
}
FlagRegistrar& OnUpdate(flags_internal::FlagCallback cb) && {
flag_->SetCallback(cb);
return *this;
}
// Make the registrar "die" gracefully as a bool on a line where registration
// happens. Registrar objects are intended to live only as temporary.
operator bool() const { return true; } // NOLINT
private:
Flag<T>* flag_; // Flag being registered (not owned).
};
// This struct and corresponding overload to MakeDefaultValue are used to
// facilitate usage of {} as default value in ABSL_FLAG macro.
struct EmptyBraces {};
template <typename T>
T* MakeFromDefaultValue(T t) {
return new T(std::move(t));
}
template <typename T>
T* MakeFromDefaultValue(EmptyBraces) {
return new T;
}
} // namespace flags_internal
} // namespace absl
#endif // ABSL_FLAGS_INTERNAL_FLAG_H_
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