Class Vs typedef

R in nutshell

pg 99 attributes

https://stats.stackexchange.com/questions/3212/mode-class-and-type-of-r-objects

https://stat.ethz.ch/R-manual/R-devel/doc/manual/R-lang.html#Objects

https://stackoverflow.com/questions/35445112/what-is-the-difference-between-mode-and-class-in-r

https://stat.ethz.ch/R-manual/R-devel/library/base/html/mode.html