Title:       Acyclic Visitor

Author:      Robert C. Martin
Email:       rmartin@oma.com
Address:     14619 N. Somerset Circle, Green Oaks, IL, 60048
Phone:       847.918.1004
Fax:         847.918.1023

The Visitor Pattern allows new functions to be added to existing
hierarchies without affecting those hierarchies.  However, in static
languages like C++, Java and Eiffel, Visitor creates a dependency
cycle that causes the base class of the hierarchy to depend upon all
its derivatives.  This paper presents a variation of the Visitor
pattern that breaks that dependency cycle by making use of multiple
inheritance and run time type information.