R classes with references resources

https://stat.ethz.ch/R-manual/R-devel/library/methods/html/refClass.html
http://adv-r.had.co.nz/OO-essentials.html
https://www.bioconductor.org/help/course-materials/2010/HeidelbergNovember2010/ReferenceClasses-Morgan.pdf

or type in R
?ReferenceClasses