Class iterator

modules/engine/graphics/src/d3d12/D3D12MemAlloc.cpp:1814–1840

    class reverse_iterator;
    class const_reverse_iterator;
    class iterator
    {
        friend class List<T>;
        friend class const_iterator;

    public:
        iterator() = default;
        iterator(const reverse_iterator& src)
            : m_pList(src.m_pList), m_pItem(src.m_pItem) {}

        T& operator*() const;
        T* operator->() const;

        iterator& operator++();
        iterator& operator--();
        iterator operator++(int);
        iterator operator--(int);

        bool operator==(const iterator& rhs) const;
        bool operator!=(const iterator& rhs) const;

    private:
        List<T>* m_pList = NULL;
        Item* m_pItem = NULL;

        iterator(List<T>* pList, Item* pItem) : m_pList(pList), m_pItem(pItem) {}
    };

    class reverse_iterator
    {