I've written a small package for logging, I'm distributing it through r-forge, recently I received some very interesting feedback on how to make it easier to use, but this functionality is based on stuff (setRefClass) that was added to R in 2.12.

I'd like to keep distributing the package also for R-2.9, so I'm looking for a way to include or exclude the S4 syntactical sugar automatically, and include it when the library is loaded on a R >= 2.12 system.

one other option I see, that is to write a small S4 package that needs 2.12, imports the simpler logging package and exports the syntactically sugared interface... I don't like it too much, as I'd need to choose a different name for the S4 package.