CSC/ECE 517 Fall 2012/ch2b 2w51 aa

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Visitor Pattern, Directory of sites

The Purpose of this article is to act as a "directory of sites", or a simple quick jump page for the reader. The effort is to try and collect good sources (blog posts, forum chats, general articles etc.) which deal with the Visitor pattern and to make this available to the readers with summary. The readers can then explore the links provided, to understand certain topics that they are interested in. Readers are also encouraged to edit the document in case they are able to contribute good material. Since this is just a quick jump page, there will be an apparent lack of examples. This is in line with the requirements given in the writeup, since we are re-directing you to pages where you will get plenty of information.

Introduction

In Object Oriented Programming, the Visitor Pattern is a way of decoupling algorithms to be performed by an object. The way to do this is to 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.

For more information on the Visitor pattern, you can visit the following links

Motivation

Now that some information is present about what the Visitor pattern is and what it should do, let us explore the motivation behind using the Visitor pattern. Some links are provided for the reader to explore the topic and a brief summary is presented to guide the reader

  • http://www.oodesign.com/visitor-pattern.html : One of the top visited sites for design pattern basics , oodesign.com has good introduction, examples and implementation details. Sample code is also available for the reader. The article is good not only from the point of view of explaining the motivation behind Visitor patterns, but also because it follows a good flow in setting up the topic, explanation using examples and concluding with a brief summary
  • 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.

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++:

Visitor Pattern in Python

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

Visitor Pattern in Ruby

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

Advantages

Disadvantages



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