Hi, FWIW what's discussed here is known as multi-methods in some corners of programming world. A multi-method with one "virtual" argument would simply be a virtual function outside a class, which is probably what the original poster was looking for. Some relatively dynamic languages, e.g. clos and dylan, support multi-methods as a native concept. I believe there have been past discussions on multi-methods in boost. I believe at least Jesse Jones was involved in one discussion thread around September 2004. I implemented multi-methods for C++ long time ago as a library. We've used them in one data visualisation project, but not really otherwise. See the links below for some documentation and examples. I doubt that particular library in the form boost would like to have, but perhaps it gives you ideas to take further. Note that the code is GPLed. http://cmslxr.fnal.gov/lxr/source/Iguana/Utilities/classlib/utils/ MultiMethod.h#093 http://cmslxr.fnal.gov/lxr/source/Iguana/Utilities/test/utils/ MultiMethod01.cpp http://cmslxr.fnal.gov/lxr/source/Iguana/Utilities/test/utils/ MultiMethod02.cpp http://cmslxr.fnal.gov/lxr/source/Iguana/Utilities/test/utils/ MultiMethod03.cpp Lassi