```
cc <- function(...)c(...)
setGeneric("cc")
setMethod("cc", "character", function(...)paste(...))
setClassUnion("Number", c("numeric", "complex"))
setMethod("cc", "Number", function(...) sum(...))
setClass("cdate", contains = "character", representation(date = "Date"))
setClass("vdate", contains = "vector", representation(date = "Date"))
cd1 <- new("cdate", "abcdef", date = Sys.Date())
cd2 <- new("vdate", "abcdef", date = Sys.Date())
stopifnot(identical(cc(letters, character(), cd1),
paste(letters, character(), cd1))) # the "character" method
stopifnot(identical(cc(letters, character(), cd2),
c(letters, character(), cd2)))
# the default, because "vdate" doesn't extend "character"
stopifnot(identical(cc(1:10, 1+1i), sum(1:10, 1+1i))) # the "Number" method
stopifnot(identical(cc(1:10, 1+1i, TRUE), c(1:10, 1+1i, TRUE))) # the default
stopifnot(identical(cc(), c())) # no arguments implies the default method
setGeneric("numMax", function(...)standardGeneric("numMax"))
setMethod("numMax", "numeric", function(...)max(...))
# won't work for complex data
setMethod("numMax", "Number", function(...) paste(...))
# should not be selected w/o complex args
stopifnot(identical(numMax(1:10, pi, 1+1i), paste(1:10, pi, 1+1i)))
stopifnot(identical(numMax(1:10, pi, 1), max(1:10, pi, 1)))
try(numMax(1:10, pi, TRUE)) # should be an error: no default method
## A generic version of paste(), dispatching on the "..." argument:
setGeneric("paste", signature = "...")
setMethod("paste", "Number", function(..., sep, collapse) c(...))
stopifnot(identical(paste(1:10, pi, 1), c(1:10, pi, 1)))
```

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