Is it possible to define object classes that have own methods in R [closed]

Question

I'd like to define a new object class in R that comes with own functionality (e.g. getter for maximum value). Is it possible to realize this in R? I was thinking of something like:

test <- class() {
  len = 0     # object variable1

  __constructor(length=0) {
    len = length # set len
  }

  getLength <- function() {
    len   # return len
  }
}

and

ob = test(20)    # create Objectof class test
ob.getLength()   # get Length-Value of Object

Answer 1

To get you started, I'll give an example with S3 classes:

# create an S3 class using setClass:
setClass("S3_class", representation("list"))
# create an object of S3_class
S3_obj <- new("S3_class", list(x=sample(10), y=sample(10)))

Now, you can function-overload internal functions, for example, length function to your class as (you can also operator-overload):

length.S3_class <- function(x) sapply(x, length)
# which allows you to do:
length(S3_obj)

#  x  y 
# 10 10 

Or alternatively, you can have your own function with whatever name, where you can check if the object is of class S3_class and do something:

len <- function(x) { 
    if (class(x) != "S3_class") {
        stop("object not of class S3_class")
    }
    sapply(x, length)
}

> len(S3_obj)
#  x  y 
# 10 10 

> len(1:10)
# Error in len(1:10) : object not of class S3_class

It is a bit hard to explain S4 (like S3) as there are quite a bit of terms and things to know of (they are not difficult, just different). I suggest you go through the links provided under comments for those (and for S3 as well, as my purpose here was to show you an example of how it's done).