copyable_ptr.h | Explore in Territory

/*
 * Copyright (C) 2019 The Android Open Source Project
 *
 * 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
 *
 *      http://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 INCLUDE_PERFETTO_PROTOZERO_COPYABLE_PTR_H_
#define INCLUDE_PERFETTO_PROTOZERO_COPYABLE_PTR_H_

#include <memory>

namespace protozero {

// This class is essentially a std::vector<T> of fixed size = 1.
// It's a pointer wrapper with deep copying and deep equality comparison.
// At all effects this wrapper behaves like the underlying T, with the exception
// of the heap indirection.
// Conversely to a std::unique_ptr, the pointer will be always valid, never
// null. The problem it solves is the following: when generating C++ classes
// from proto files, we want to keep each header hermetic (i.e. not #include
// headers of dependent types). As such we can't directly instantiate T
// field members but we can instead rely on pointers, so only the .cc file needs
// to see the actual definition of T. If the generated classes were move-only we
// could just use a unique_ptr there. But they aren't, hence this wrapper.
// Converesely to unique_ptr, this wrapper:
// - Default constructs the T instance in its constructor.
// - Implements deep comparison in operator== instead of pointer comparison.
template <typename T>
class CopyablePtr { … };

}  // namespace protozero

#endif  // INCLUDE_PERFETTO_PROTOZERO_COPYABLE_PTR_H_
chromium/third_party/perfetto/include/perfetto/protozero/copyable_ptr.h
