---
layout: pattern
title: Acyclic Visitor
folder: acyclic-visitor
permalink: /patterns/acyclic-visitor/
categories: Behavioral
tags:
 - Java
 - Difficulty-Intermediate
---

![alt text](./etc/acyclic-visitor.png "Acyclic Visitor")

## Intent
Allow new functions to be added to existing class hierarchies without affecting those hierarchies, and without creating the troublesome dependency cycles that are inherent to the GOF VISITOR Pattern.

## Applicability
This pattern can be used:
* When you need to add a new function to an existing hierarchy without the need to alter or affect that hierarchy.
* When there are functions that operate upon a hierarchy, but which do not belong in the hierarchy itself. e.g. the ConfigureForDOS / ConfigureForUnix / ConfigureForX issue.
* When you need to perform very different operations on an object depending upon its type.
* When the visited class hierarchy will be frequently extended with new derivatives of the Element class.
* When the recompilation, relinking, retesting or redistribution of the derivatives of Element is very expensive.

## Related patterns
* [Visitor Pattern](../visitor/README.md)

## Credits
* [Acyclic Visitor](http://condor.depaul.edu/dmumaugh/OOT/Design-Principles/acv.pdf)