cc: Switch ListContainer to use composition instead of inheritance.

cc/base/list_container_helper.h

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CC_BASE_LIST_CONTAINER_HELPER_H_
+#define CC_BASE_LIST_CONTAINER_HELPER_H_
+
+#include "base/memory/scoped_ptr.h"
+#include "cc/base/cc_export.h"
+
+namespace cc {
+
+// Helper class for ListContainer non-templated logic. All methods are private,
+// and only exposed to friend classes.
+// For usage, see comments in ListContainer (list_container.h).
+class CC_EXPORT ListContainerHelper final {
+ private:
+  template <typename T>
+  friend class ListContainer;
+
+  explicit ListContainerHelper(size_t max_size_for_derived_class);
+  ListContainerHelper(size_t max_size_for_derived_class,
+                      size_t num_of_elements_to_reserve_for);
+  ~ListContainerHelper();
+
+  // This class deals only with char* and void*. It does allocation and passing
+  // out raw pointers, as well as memory deallocation when being destroyed.
+  class CharAllocator;
+
+  // This class points to a certain position inside memory of
+  // CharAllocator. It is a base class for ListContainer iterators.
+  struct CC_EXPORT PositionInCharAllocator {
+    CharAllocator* ptr_to_container;
+    size_t vector_index;
+    char* item_iterator;
+
+    PositionInCharAllocator(const PositionInCharAllocator& other);
+
+    PositionInCharAllocator(CharAllocator* container,
+                            size_t vector_ind,
+                            char* item_iter);
+
+    bool operator==(const PositionInCharAllocator& other) const;
+    bool operator!=(const PositionInCharAllocator& other) const;
+
+    PositionInCharAllocator Increment();
+    PositionInCharAllocator ReverseIncrement();
+  };
+
+  // Iterator classes that can be used to access data.
+  /////////////////////////////////////////////////////////////////
+  class CC_EXPORT Iterator : public PositionInCharAllocator {
+    // This class is only defined to forward iterate through
+    // CharAllocator.
+   public:
+    Iterator(CharAllocator* container,
+             size_t vector_ind,
+             char* item_iter,
+             size_t index);
+    ~Iterator();
+
+    size_t index() const;
+
+   protected:
+    // This is used to track how many increment has happened since begin(). It
+    // is used to avoid double increment at places an index reference is
+    // needed. For iterator this means begin() corresponds to index 0 and end()
+    // corresponds to index |size|.
+    size_t index_;
+  };
+
+  class CC_EXPORT ConstIterator : public PositionInCharAllocator {
+    // This class is only defined to forward iterate through
+    // CharAllocator.
+   public:
+    ConstIterator(CharAllocator* container,
+                  size_t vector_ind,
+                  char* item_iter,
+                  size_t index);
+    ConstIterator(const Iterator& other);  // NOLINT
+    ~ConstIterator();
+
+    size_t index() const;
+
+   protected:
+    // This is used to track how many increment has happened since begin(). It
+    // is used to avoid double increment at places an index reference is
+    // needed. For iterator this means begin() corresponds to index 0 and end()
+    // corresponds to index |size|.
+    size_t index_;
+  };
+
+  class CC_EXPORT ReverseIterator : public PositionInCharAllocator {
+    // This class is only defined to reverse iterate through
+    // CharAllocator.
+   public:
+    ReverseIterator(CharAllocator* container,
+                    size_t vector_ind,
+                    char* item_iter,
+                    size_t index);
+    ~ReverseIterator();
+
+    size_t index() const;
+
+   protected:
+    // This is used to track how many increment has happened since rbegin(). It
+    // is used to avoid double increment at places an index reference is
+    // needed. For reverse iterator this means rbegin() corresponds to index 0
+    // and rend() corresponds to index |size|.
+    size_t index_;
+  };
+
+  class CC_EXPORT ConstReverseIterator : public PositionInCharAllocator {
+    // This class is only defined to reverse iterate through
+    // CharAllocator.
+   public:
+    ConstReverseIterator(CharAllocator* container,
+                         size_t vector_ind,
+                         char* item_iter,
+                         size_t index);
+    ConstReverseIterator(const ReverseIterator& other);  // NOLINT
+    ~ConstReverseIterator();
+
+    size_t index() const;
+
+   protected:
+    // This is used to track how many increment has happened since rbegin(). It
+    // is used to avoid double increment at places an index reference is
+    // needed. For reverse iterator this means rbegin() corresponds to index 0
+    // and rend() corresponds to index |size|.
+    size_t index_;
+  };
+
+  // Unlike the ListContainer methods, these do not invoke element destructors.
+  void RemoveLast();
+  void EraseAndInvalidateAllPointers(Iterator* position);
+  void InsertBeforeAndInvalidateAllPointers(Iterator* position,
+                                            size_t number_of_elements);
+
+  ConstReverseIterator crbegin() const;
+  ConstReverseIterator crend() const;
+  ReverseIterator rbegin();
+  ReverseIterator rend();
+  ConstIterator cbegin() const;
+  ConstIterator cend() const;
+  Iterator begin();
+  Iterator end();
+
+  Iterator IteratorAt(size_t index);
+  ConstIterator IteratorAt(size_t index) const;
+
+  size_t size() const;
+  bool empty() const;
+
+  size_t MaxSizeForDerivedClass() const;
+
+  size_t GetCapacityInBytes() const;
+
+  // Unlike the ListContainer method, this one does not invoke element
+  // destructors.
+  void clear();
+
+  size_t AvailableSizeWithoutAnotherAllocationForTesting() const;
+
+  // Hands out memory location for an element at the end of data structure.
+  void* Allocate(size_t size_of_actual_element_in_bytes);
+
+  scoped_ptr<CharAllocator> data_;
+
+  DISALLOW_COPY_AND_ASSIGN(ListContainerHelper);
+};
+
+}  // namespace cc
+
+#endif  // CC_BASE_LIST_CONTAINER_HELPER_H_