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1// Copyright 2020 the V8 project authors. All rights reserved.2// Use of this source code is governed by a BSD-style license that can be3// found in the LICENSE file.4 5#ifndef INCLUDE_CPPGC_GARBAGE_COLLECTED_H_6#define INCLUDE_CPPGC_GARBAGE_COLLECTED_H_7 8#include "cppgc/internal/api-constants.h"9#include "cppgc/platform.h"10#include "cppgc/trace-trait.h"11#include "cppgc/type-traits.h"12 13namespace cppgc {14 15class Visitor;16 17/**18 * Base class for managed objects. Only descendent types of `GarbageCollected`19 * can be constructed using `MakeGarbageCollected()`. Must be inherited from as20 * left-most base class.21 *22 * Types inheriting from GarbageCollected must provide a method of23 * signature `void Trace(cppgc::Visitor*) const` that dispatchs all managed24 * pointers to the visitor and delegates to garbage-collected base classes.25 * The method must be virtual if the type is not directly a child of26 * GarbageCollected and marked as final.27 *28 * \code29 * // Example using final class.30 * class FinalType final : public GarbageCollected<FinalType> {31 *  public:32 *   void Trace(cppgc::Visitor* visitor) const {33 *     // Dispatch using visitor->Trace(...);34 *   }35 * };36 *37 * // Example using non-final base class.38 * class NonFinalBase : public GarbageCollected<NonFinalBase> {39 *  public:40 *   virtual void Trace(cppgc::Visitor*) const {}41 * };42 *43 * class FinalChild final : public NonFinalBase {44 *  public:45 *   void Trace(cppgc::Visitor* visitor) const final {46 *     // Dispatch using visitor->Trace(...);47 *     NonFinalBase::Trace(visitor);48 *   }49 * };50 * \endcode51 */52template <typename T>53class GarbageCollected {54 public:55  using IsGarbageCollectedTypeMarker = void;56  using ParentMostGarbageCollectedType = T;57 58  // Must use MakeGarbageCollected.59  void* operator new(size_t) = delete;60  void* operator new[](size_t) = delete;61  // The garbage collector is taking care of reclaiming the object. Also,62  // virtual destructor requires an unambiguous, accessible 'operator delete'.63  void operator delete(void*) {64#ifdef V8_ENABLE_CHECKS65    internal::Fatal(66        "Manually deleting a garbage collected object is not allowed");67#endif  // V8_ENABLE_CHECKS68  }69  void operator delete[](void*) = delete;70 71 protected:72  GarbageCollected() = default;73};74 75/**76 * Base class for managed mixin objects. Such objects cannot be constructed77 * directly but must be mixed into the inheritance hierarchy of a78 * GarbageCollected object.79 *80 * Types inheriting from GarbageCollectedMixin must override a virtual method81 * of signature `void Trace(cppgc::Visitor*) const` that dispatchs all managed82 * pointers to the visitor and delegates to base classes.83 *84 * \code85 * class Mixin : public GarbageCollectedMixin {86 *  public:87 *   void Trace(cppgc::Visitor* visitor) const override {88 *     // Dispatch using visitor->Trace(...);89 *   }90 * };91 * \endcode92 */93class GarbageCollectedMixin {94 public:95  using IsGarbageCollectedMixinTypeMarker = void;96 97  // Must use MakeGarbageCollected.98  void* operator new(size_t) = delete;99  void* operator new[](size_t) = delete;100  // The garbage collector is taking care of reclaiming the object.101  // Not override the non-array varaint of `delete` to not conflict with the102  // operator in GarbageCollected above.103  void operator delete[](void*) = delete;104 105  /**106   * This Trace method must be overriden by objects inheriting from107   * GarbageCollectedMixin.108   */109  virtual void Trace(cppgc::Visitor*) const {}110};111 112}  // namespace cppgc113 114#endif  // INCLUDE_CPPGC_GARBAGE_COLLECTED_H_115