[R] S4 newbie - extending S3 classes

[Tim Bergsma]

I tried recently to extend data.frame using S4, with depressing results. 
  Someone asked about this back in January, and was referred to the 
"Register or Convert" advice.  Putting the pieces together, I'm guessing 
  that to extend data.frame usefully in S4, one would actually have to 
write it from scratch, creating all the usual attributes, methods, etc. 
  One certainly wouldn't want to do this if unnecessary or if already 
done by someone more competent.  I've ordered John Chamber's book 
"Programming with Data".  In the meantime, can someone confirm/deny my 
suspicions that data.frame would need an S4 rewrite and that no standard 
rewrite exists?

Thanks,

Tim.