Learning the programming in the new S4 system of classes and methods in R can be quite cumbersome, even though the methods package is very well documented. That is why I collected some of the info and materials that I am aware of on a separate page here. I warmly welcome any suggestions for extending this, for now short, collection!

Where to look for information on programming with S4 system of classes and methods for R? Here is a open-ended collection of links to resources on learning programming in S4 system. Suggestions more than welcome!
Books

• John M. Chambers. Programming with Data. Springer, New York, 1998. ISBN 0-387-98503-4. Some more info here http://cm.bell-labs.com/cm/ms/departments/sia/Sbook/
• John M. Chambers. Software for Data Analysis: Programming with R. Springer, New York, 2008. ISBN 0387759352, 9780387759357.

Articles and notes

• Short note by John Chambers “Classes and Methods in the S Language” [PDF] www.omegahat.org/RSMethods/Intro.pdf
• Another note by John Chambers “S4 Classes in 15 pages, more or less” [PDF]www.stat.ucla.edu/~cocteau/stat202a/resources/docs/S4Objects.pdf

Presentation slides

• Slides by Friedrich Leisch from UseR! 2004 conference in Vienna [PDF] http://www.ci.tuwien.ac.at/Conferences/useR-2004/Keynotes/Leisch.pdf

Links

• On R Wiki http://wiki.r-project.org/rwiki/doku.php?id=tips:classes-s4
• http://www.omegahat.org/RSMethods/

Packages

Sometimes it is worthwhile to look at the source code of the available packages and learn from that. Here is are the packages that can be instructive: stats4, lme4.