Composites-Visitors pattern: the OOP way

//Tree.h
#pragma once
#include "RefCnt.h"

namespace GE_{ namespace NTypes{

	//ITreeNode: interface for composite objects

	interface ITreeNode:
		public virtual IReferable
	{
		virtual ITreeNode* GetFirstChild()=0;
		virtual ITreeNode* GetLastChild()=0;
		virtual int GetChildrenCount()=0;
		virtual ITreeNode* GetParent()=0;
		virtual ITreeNode* GetPrev()=0;
		virtual ITreeNode* GetNext()=0;
		virtual bool SetParent(ITreeNode* pParent, ITreeNode* pPrevious=NULL)=0;
		virtual ~ITreeNode() {}
	
        typedef NTypes::Ptr<ITreeNode, IReferable::XPtr> Ptr;
	protected:
		//function for use by implementors
		virtual void SetFirstChild(ITreeNode*)=0;
		virtual void SetLastChild(ITreeNode*)=0;
		virtual void SetPrev(ITreeNode*)=0;
		virtual void SetNext(ITreeNode*)=0;
		virtual void ChangeChildrenCount(int delta)=0;
		struct XProxy
		{
			ITreeNode* _pN;
			XProxy(ITreeNode* pN) { _pN = pN; }
			void SetFirstChild(ITreeNode* pN) {_pN->SetFirstChild(pN); }
			void SetLastChild(ITreeNode* pN) {_pN->SetLastChild(pN); }
			void SetPrev(ITreeNode* pN) {_pN->SetPrev(pN); }
			void SetNext(ITreeNode* pN) {_pN->SetNext(pN); }
			void ChangeChildrenCount(int delta) {_pN->ChangeChildrenCount(delta); }
		};
		friend XProxy;

	protected:
		struct XShallowIterate
		{
		protected:
			typedef ITreeNode _TRefType;
			void _assign(ITreeNode* p);
			ITreeNode* _access() const;
			void _inc();
			void _dec();
			ITreeNode* _subscript(int i);

		protected:
			ITreeNode::Ptr _pCurrent;
		};
	public:
		typedef NTypes::Ptr<ITreeNode, XShallowIterate> ItShallow;

	protected:
		struct XDeepIterate: public XShallowIterate
		{
			void _inc();
			void _dec();
		};
	public:
		typedef NTypes::Ptr<ITreeNode, XDeepIterate> ItDeep;

	};

	class ETreeNode: 
		public virtual ITreeNode,
		public virtual EReferable
	{
	public:
		virtual ITreeNode* GetFirstChild();
		virtual ITreeNode* GetLastChild();
		virtual ITreeNode* GetParent();
		virtual ITreeNode* GetPrev();
		virtual ITreeNode* GetNext();
		virtual int GetChildrenCount();
		virtual bool SetParent(ITreeNode* pParent, ITreeNode* pPrevious=NULL);
	protected:
		virtual void SetFirstChild(ITreeNode* pN);
		virtual void SetLastChild(ITreeNode* pN);
		virtual void SetPrev(ITreeNode* pN);
		virtual void SetNext(ITreeNode* pN);
		virtual void ChangeChildrenCount(int delta);
	protected:
		//hooks
		virtual bool OnSettingParent(ITreeNode* pParent, ITreeNode* pPrevious) {return true;}
		virtual void OnSettedParent() {}
	private:
		ITreeNode::Ptr _pChildFirst, _pChildLast, _pNext;
		ITreeNode *_pParent, *_pPrev; //backpointers don't refcount.
		int _nCount;
	protected:
		ETreeNode();
		virtual ~ETreeNode();
	};

}}