CSC/ECE 517 Fall 2012/ch2b 2w51 aa

Visitor Pattern, Directory of sites

Introduction

In Object Oriented Programming, visitor pattern is a way of decoupling algorithms to be performed by an object. The way to do this is create a visitor class which would help to add new virtual function to the classes without modifying their structures. This is accomplished by creating appropriate specializations of the virtual function in visitor class which will take instance reference as input and implements the algorithm using double dispatch.

• http://kasunpanorama.blogspot.com/2010/04/understanding-visitor-pattern.html This page can provide more introductory information on visitor pattern

Motivation

• http://en.wikipedia.org/wiki/Visitor_pattern - Motivation for visitor patterns is nicely depicted in Wikipedia for Visitor pattern.

• http://www.oodesign.com/visitor-pattern.html - One of the top visited sites for design pattern basics to implementation, oodesign.com has good introduction, implementation details.

• http://sourcemaking.com/design_patterns/visitor This page has good detailed description of visitor pattern and the worth reading part is the discussion section of this page which also talks about how double dispatch is related to visitor.

• http://www.dofactory.com/Patterns/PatternVisitor.aspx - Simple introductory page which describes and talks about the pattern in short.

Visitor Pattern in Java

(1) http://java.dzone.com/articles/design-patterns-visitor (2) http://www.javaworld.com/javatips/jw-javatip98.html (3) http://snehaprashant.blogspot.com/2009/01/visitor-pattern-in-java.html (4) http://en.wikipedia.org/wiki/Visitor_pattern#Java_example

Visitor Pattern in C++

Following are the links which provides examples based on C++:

• http://sourcemaking.com/design_patterns/visitor/cpp/1

• http://sourcemaking.com/design_patterns/visitor/cpp/3

• http://sourcemaking.com/design_patterns/visitor/cpp/2

• This page explains visitor pattern in detail from the basics upto implementation using C++ as language. It has implementation details and also have discussed issues that arise. http://www.swe.uni-linz.ac.at/research/deco/designPatterns/visitor/visitor.defaultroles.c++.html

Visitor Pattern in Python

Following are two links which provide good examples of implementation of visitor patterns in python:

• https://chris-lamb.co.uk/2006/12/08/visitor-pattern-in-python/

• http://curtis.schlak.com/2012/01/04/python-visitor-pattern-helper.html

Visitor Pattern in Ruby

(1) https://gist.github.com/989193 (2) http://www.scribd.com/doc/2217773/Design-Patterns-in-Ruby

Advantages

• This links helps to understand the advantage of a design pattern like visitor, which are the features it combines and how it makes it easy for programmer to implement those ideas. http://compilers.cs.ucla.edu/jtb/jtb-2003/whyvisitors/whyvisitors.html

• The applicability of visitor pattern can be found here: http://www.swe.uni-linz.ac.at/research/deco/designPatterns/visitor/visitor.abstract.html#Applicability

Disadvantages

• http://www.developerfusion.com/article/84939/iterators-composites-and-visitors/ This page has a subsection in the visitor pattern section which discusses issues related to visitor pattern.

• http://www.oodesign.com/visitor-pattern.html This page describes issues with visitor pattern in section Specific problems and implementation

Video Lecture: (1) https://www.youtube.com/watch?v=mTJodk3vfdk (2) https://www.youtube.com/watch?v=UYUopyMcWjw&feature=related