setattr(obj, "class", CLASS)); can add instead of replaceSets the class of an object in place to cl
by replacing or adding
setclass(obj, cl, add = FALSE, add.place = "first")and object for which to set class
class to set
if TRUE, adds cl to the 
classes of the obj; otherwise replaces the class information
"first" or "last"; adds cl
to the front or to the back of the obj's class vector