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Posted 7 Aug 2004

Composites and Visitors - a Templatised Approach

, 13 Oct 2004
An article on a templatised implementation of composite and visitor interaction.
// composites_visitors.cpp : Defines the entry point for the console application.

#include "stdafx.h"
#include "NodeBase.h"
#include "VisitorBase.h"

#include <iostream>

using namespace std;

int _tmain(int argc, _TCHAR* argv[])
	// Set up a simple composite tree
	CNodeBase *head = new CNodeBase;
	CNodeBase *child1 = new CNodeDerived1;
	head->push_back( child1 );
	CNodeBase *child2 = new CNodeDerived2;
	head->push_back( child2 );
	child1->push_back( new CNodeDerived1 );
	child1->push_back( new CNodeDerived2 );
	child2->push_back( new CNodeDerived2 );
	child2->push_back( new CNodeDerived1 );
	child2->push_back( new CNodeBase );

	// Examples of shallow iterators
	cout << "Shallow Iteration from Head" << endl;
	CNodeBase::shallow_iterator iter1 = head->begin_shallow();
	for ( ; iter1 != head->end_shallow(); ++iter1 )
		cout << (*iter1)->GetId() << " " << (*iter1)->GetType() << endl;
	cout << "Shallow Iteration from Child2" << endl;
	for ( iter1 = child2->begin_shallow(); iter1 != child2->end_shallow(); ++iter1 )
		cout << (*iter1)->GetId() << " " << (*iter1)->GetType() << endl;
	// Examples of deep iterators
	cout << "Deep Iteration from Head" << endl;
	CNodeBase::deep_iterator iter2 = head->begin_deep();
	for ( ; iter2 != head->end_deep(); ++iter2 )
		cout << (*iter2)->GetId() << " " << (*iter2)->GetType() << endl;
	cout << "Deep Iteration from Child1" << endl;
	for ( iter2 = child1->begin_deep(); iter2 != child1->end_deep(); ++iter2 )
		cout << (*iter2)->GetId() << " " << (*iter2)->GetType() << endl;

	// Examples of visitors
	cout << "Visiting entire tree using a top to bottom strategy" << endl;
	CVisitorDerived1TopToBottom visitor1;
	visitor1( head );
	cout << "Visiting entire tree using a bottom to top strategy" << endl;
	CVisitorDerived2BottomToTop visitor2;
	visitor2( head );
	cout << "Visiting entire tree using a left to right strategy" << endl;
	CVisitorDerived2LeftToRight visitor3;
	visitor3( head );

	// Wait for user to hit something
	char c;
	cin >> c;

	return 0;

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About the Author

Dave Handley
Web Developer
United Kingdom United Kingdom
I started programming on 8 bit machines as a teenager, writing my first compiled programming language before I was 16. I went on to study Engineering and Computer Science at Oxford University, getting a first and the University Prize for the best results in Computer Science. Since then I have worked in a variety of roles, involving systems management and development management on a wide variety of platforms. Now I manage a software development company producing CAD software for Windows using C++.

My 3 favourite reference books are: Design Patterns, Gamma et al; The C++ Standard Library, Josuttis; and Computer Graphics, Foley et al.

Outside computers, I am also the drummer in a band, The Unbelievers and we have just released our first album. I am a pretty good juggler and close up magician, and in my more insane past, I have cycled from Spain to Eastern Turkey, and cycled across the Namib desert.

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