library(methods)

## Class definitions

#' Represents a circle shape
#'
#' @param r radius of the circle
#'
#' @returns S4 object
#' @export
circleS4 <- setClass("circleS4", slots = list(r = "numeric"))

#' Represents a rectangle shape
#'
#' @param w width of the rectangle
#' @param h height of the rectangle
#'
#' @returns S4 object
#' @export
rectangleS4 <- setClass("rectangleS4", slots = list(w = "numeric", h = "numeric"))


## setting class methods
# redefine generic methods
setMethod("show", "circleS4", function(object) {
    cat("< circle r =", object@r, ">\n")
})
setMethod("show", signature="rectangleS4", function(object) {
    cat("<rectangle w =", rect@w, ", h =", rect@h, ">\n", set="")
})

## define new generics for class assignement
# create a method to assign the value of a coordinate
setGeneric("area", def = function(object) standardGeneric("area") )
setGeneric(name = "diam", def = function(object) {
    standardGeneric("diam")
})

## assigne (custom) generics implementation to classes
setMethod("area", "circleS4", function(object) pi * object@r^2)
setMethod("diam", "circleS4", function(object) 2 * object@r)

setMethod("area", signature=list(object = "rectangleS4"), function(object) {
    object@w * object@h
})
setMethod("diam", signature=list(object = "rectangleS4"), function(object) {
    sqrt(rect@w^2 + rect@h^2)
})

# usage
circ <- circleS4(r = 2)
rect <- rectangleS4(w = 1, h = 2)

print(area(circ))
print(diam(rect))

print(circ)
print(rect)