http://adv-r.had.co.nz/OO-essentials.html#s4 - "All S4 related code is stored in the methods package. This package is always available when you’re running R interactively, but may not be available when running R in batch mode. For this reason, it’s a good idea to include an explicit library(methods) whenever you’re using S4."
http://adv-r.had.co.nz/OO-essentials.html#s4 - "All S4 related code is stored in the methods package. This package is always available when you’re running R interactively, but may not be available when running R in batch mode. For this reason, it’s a good idea to include an explicit library(methods) whenever you’re using S4."