Help an oop newbie

[startz]

Hi folks, I am trying to learn a bit of how to extend R using object oriented programming. I set myself a little task to extend numerics so that if the value equals 7 "little bunny foo foo" will be printed. In other cases, the actual value will be printed. My code is

new_nursery_Song <- function(x = double()){
  stopifnot(is.double(x))
  structure(x,class = c("nursery_Song","numeric"))
}

print.nursery_Song <- function(x){
  if (x == 7)
    print("little bunny foo foo")
  else
    print(x)
}
print(new_nursery_Song(7))
print(new_nursery_Song(3))

which gives

[1] "little bunny foo foo"
Error: C stack usage  15927136 is too close to the limit

(My guess is that print() is being called recursively rather than going to the generic print(), but it's just a guess.)

Any help will be greatly appreciated, including telling me that I'm thinking about this entirely in the wrong way. By way of background,

1. It's been a long time since I've done any object oriented programming.
2. I've never done oop in R (which you've probably already guessed).

I have read through the relevant parts of both Hands on Programming with R (Grolemund) and Advanced R (Wickham). Both quite helpful.

[nirgrahamuk]

@startz

(My guess is that print() is being called recursively rather than going to the generic print(), but it's just a guess.)

This is correct, when x is not 7 it will endlessly try to call print.nursery_Song, to fix have it use the default print for numeric, like so

new_nursery_Song <- function(x = double()){
  stopifnot(is.double(x))
  structure(x,class = c("nursery_Song","numeric"))
}

print.nursery_Song <- function(x){
  if (x == 7)
"little bunny foo foo"
  else
    print(as.numeric(x))
}
print(new_nursery_Song(7))
print(new_nursery_Song(3))

[startz]

Thanks @nirgrahamuk, that solves my problem. Since I'm mostly doing this to learn, any more guidance or pointers on how to think about inheritance?