From henrikb@braju.com  Mon Jul 16 07:52:14 2001
From: henrikb@braju.com (Henrik Bengtsson)
Date: Sun, 15 Jul 2001 23:52:14 -0700
Subject: [Rd] Function calls and UseMethod.
Message-ID: <KKEGJOGBELBHDIKPINBMCEHFCFAA.henrikb@braju.com>

Maybe the following have already been discussed, if not...

BACKGROUND: I am writing a class which should have the method get(). For
this (and a lot of other things) to work I have to redefine the default
get() like this:

if (!exists("get.default")) get.default <- get;
get <- function(obj, ...) {
  if (missing(obj) obj <- NULL;
  UseMethod("get", obj, ...);
}

and still I am not sure if this is bullet proof. Maybe someone else, i.e. in
a previously loaded library, has already modified the get() method.

SUGGESTION I: Would it be possible to have *all* function calls by default
using the UseMethod approach? What I suggest results in that there is no
need for people to actually write the UseMethod function wrappers, but it
should be done within [R]. Example:

myHelloWorld.default <- function() {
  cat("Hello world!\n");
}

and this should be able to be called just as

myHelloWorld()

without having to explicitly write

myHelloWorld <- function(obj, ...) {
  if (missing(obj) obj <- NULL;
  UseMethod("myHelloWorld", obj, ...)
}

I think this could clean up a lot of the "mess" of overloading and
redefining functions. It would also definitely remove on risk of overwriting
allready existing functions. I can see some problems how to implement this;
for instance, how would [R] know that myHelloWorld is a function call? I
know too little about the internal structure.

SUGGESTION II: If the first approach is not possible, what about "cleaning
up" the [R] code (base etc) and always write like get.default declarations
and not just get? Is there a reason not to?

Thanks

Henrik Bengtsson

150 Panoramic Way
Berkeley, CA 94704
(510) 647-3572
h e n r i k b @ b r a j u . c o m

PS. For some reason I mailed this message to r-announce-request@lists...
before. Sorry about that. DS.

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[Rd] Function calls and UseMethod.
Henrik Bengtsson