nullstream.h | Explore in Territory

// Copyright 2022 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: log/internal/nullstream.h
// -----------------------------------------------------------------------------
//
// Classes `NullStream`, `NullStreamMaybeFatal ` and `NullStreamFatal`
// implement a subset of the `LogMessage` API and are used instead when logging
// of messages has been disabled.

#ifndef ABSL_LOG_INTERNAL_NULLSTREAM_H_
#define ABSL_LOG_INTERNAL_NULLSTREAM_H_

#ifdef _WIN32
#include <cstdlib>
#else
#include <unistd.h>
#endif
#include <ios>
#include <ostream>

#include "absl/base/attributes.h"
#include "absl/base/config.h"
#include "absl/base/log_severity.h"
#include "absl/strings/string_view.h"

namespace absl {
ABSL_NAMESPACE_BEGIN
namespace log_internal {

// A `NullStream` implements the API of `LogMessage` (a few methods and
// `operator<<`) but does nothing.  All methods are defined inline so the
// compiler can eliminate the whole instance and discard anything that's
// streamed in.
class NullStream { … };
template <typename T>
inline NullStream& operator<<(NullStream& str, const T&) { … }
inline NullStream& operator<<(NullStream& str,
                              std::ostream& (*)(std::ostream& os)) { … }
inline NullStream& operator<<(NullStream& str,
                              std::ios_base& (*)(std::ios_base& os)) { … }

// `NullStreamMaybeFatal` implements the process termination semantics of
// `LogMessage`, which is used for `DFATAL` severity and expression-defined
// severity e.g. `LOG(LEVEL(HowBadIsIt()))`.  Like `LogMessage`, it terminates
// the process when destroyed if the passed-in severity equals `FATAL`.
class NullStreamMaybeFatal final : public NullStream { … };

// `NullStreamFatal` implements the process termination semantics of
// `LogMessageFatal`, which means it always terminates the process.  `DFATAL`
// and expression-defined severity use `NullStreamMaybeFatal` above.
class NullStreamFatal final : public NullStream { … };

}  // namespace log_internal
ABSL_NAMESPACE_END
}  // namespace absl

#endif  // ABSL_LOG_INTERNAL_GLOBALS_H_
chromium/third_party/abseil-cpp/absl/log/internal/nullstream.h
