[Rd] S3 vs S4 classes

[Rossi, Peter E.]

I have developed a package, bayesm, which uses existing classes of
objects.  I would like
to add a new class corresponding to objects from this package.

I have been reading about classes and all sources tell me that I should
use
so-called "new" or S4 classes.

However, a major purpose of defining a class for my package would be to
add methods to the existing generic functions:  print, plot, and
summary.  My understanding
is that these functions work with the "old" or S3 classes.  

If I want to use S4 classes, do I need to write new generic functions or
is there
as way to "extend" the existing generics to work with S4 classes and
objects.  I may
be using the wrong word here "extend" but I hope that everyone
understands the point.
If I have to write new generic functions, it is a simply matter of
registering the pre-existing
methods based on S3 objects?  Or do you basicaly have to start from
scratch -- i.e.
the two types of classes, methods and generic functions are distinct?

thanks 

peter r
 
................................
 Peter E. Rossi
 Joseph T. and Bernice S. Lewis Professor of Marketing and Statistics
 Editor, Quantitative Marketing and Economics
 Rm 353, Graduate School of Business, U of Chicago
 5807 S. Woodlawn Ave, Chicago IL 60637
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