[R] fun with S4 method recursion

From: Ross Boylan <ross_at_biostat.ucsf.edu>
Date: Wed 08 Jun 2005 - 10:15:44 EST


Apparently using an existing function as the definition for a method is a no-no (at least as I'm doing it), producing infinite recursion. setClass("A",

         representation(model="ANY")

)

fiddle <- function(self) {
  1
}

setMethod("fiddle",

          signature(self="A"),
          definition = fiddle  ### problem
          )

setClass("B",
         representation(err="ANY"),
         contains="A"

)
setMethod("fiddle", signature(self="B"), definition = function(self){ callNextMethod() 2 })

b <- new("B", model=4, err=5)
fiddle(b)

produces
Error: protect(): protection stack overflow

On the other hand, if the line marked ### problem becomes

        definition = function(self) 1
everything works OK.

I think the definition of the generic is ending up as the method for A. This surprised me, because I thought this was the standard way to approach setting up a method ("Any ordinary function can be converted into a generic by simply setting a method for it; ... the initial, unique method (the body of the function) becomes the default method" pp. 322-323; "a generic function is created automatically by specifying a method for any existing function. This is by far the more common situation" p 348--all pages in the green book). It also surprised me because of the note that setMethod makes a local copy of the function given as the definition argument (bottom of p. 323).

Does the behavior of R differ from that described in the green book when the name of a function appears in the definition argument of setMethod? If not, what have I misunderstood?

Aside: my first real attempt didn't have

        fiddle <- function(self) {1}
using just

        setMethod("fiddle", "A", function(self) 1) That produces no existing definition for function 'fiddle'

Given all this, would this be a better model? fiddle <- function(... # definition for A # do NOT setMethod for class A signature setMethod("fiddle", "B", function(self) #operations for B So when I do the setMethod my original fiddle becomes the default generic.

Thanks.
Ross



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