R devel - Apr 2008 - methods::is problem in R 2.7.0 & R 2.8.0 devel

Hi,

x <- 1L
class(x) <- c("myInt", "integer")
is(x)
Error in inherits(x, "factor") :
  argument "class2" is missing, with no default

The problem arises when is() is used with only one argument (object)
which has more than one class reported by class(object).
In the code is() does use variable "class2" before checking for its
presence.

Reversing the order of checks

is2 <- function(object, class2) {
 cl <- class(object)
 if (missing(class2))
 return(extends(cl))
 if (length(cl) > 1)
 return(class2 %in% cl)
 if (.identC(cl, class2) || .identC(class2, "ANY"))
         return(TRUE)
     ext <- possibleExtends(cl, class2)
     if (is.logical(ext))
         ext
     else if (ext at simple)
         TRUE
     else ext at test(object)
}

is2(x)
[1] "myInt"   "integer"


This is not sufficient, though:

utils::data(npk, package="MASS")
ret <- aov(yield ~ block + N*P*K, npk)
is2(ret)
[1] "aov"      "lm"       "lm"      
"mlm"      "oldClass" "oldClass"

with duplicate class names

due to
extends(class(ret))
[1] "aov"      "lm"       "lm"      
"mlm"      "oldClass" "oldClass"

so something different would be needed.


Best,

  Matthias

> sessionInfo()
R version 2.7.0 RC (2008-04-15 r45347)
i686-pc-linux-gnu

locale:
LC_CTYPE=de_DE at
euro;LC_NUMERIC=C;LC_TIME=C;LC_COLLATE=C;LC_MONETARY=C;LC_MESSAGES=C;LC_PAPER=de_DE
at euro;LC_NAME=C;LC_ADDRESS=C;LC_TELEPHONE=C;LC_MEASUREMENT=de_DE at
euro;LC_IDENTIFICATION=C

attached base packages:
[1] stats     graphics  grDevices datasets  utils     methods   base


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Matthias Burger                     Project Manager/ Biostatistician
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