Re: [Rd] Overloading methods in R

[Ali -]

f <- function(...) UseMethod("f", NULL)
f.NULL <- function(...) {
        args <- list(...)
        classes <- sapply(args, class)
        .Class <- paste(classes, collapse = ".")
        NextMethod("f", ...)
}
f.numeric <- function(...) 2 * ..1
f.numeric.numeric <- function(...) ..1 + ..2
f.character.numeric.Date <- function(...) {
   args <- list(...)
   paste(args[[1]], args[[2]], format(args[[3]], "%Y-%m-%d"))
}
f.default <- function(...) print(list(...))
f(1)   # 2
f(1,2) # 3
f("a", 23, Sys.Date()) # "a 23 2005-04-21"
f()    # list()

Thanks Gabor! This answers a big part of my question. I am just curious why 
something like this doesn't work in S4:

-------------------------
setGeneric("foo", function(object, ...) standardGeneric("foo"))
foo.NULL <- function(object, ...) {
        args <- list(...)
        classes <- sapply(args, class)
        .Class <- paste(classes, collapse = ".")
}
foo.default <- function(object, ...) paste("wrong args!")
foo.numeric <- function(object, ...) 2 * ..1
foo.numeric.numeric <- function(object, ...) ..1 + ..2
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