[Rd] R 2.5.0 devel try issue in conjuntion with S4 method dispatch

[ml-it-r-devel at epigenomics.com]

Hi,

after updating R 2.5.0 devel yesterday we today observed many new
unexpected failures in our daily package build and test system runs,
which can be traced to recent changes in the implementation in try()
(as noted in NEWS).

Investigating this new implementation I come across an issue in
conjuntion with using S4 classes and methods. try(expr) does not return an
object with attribute 'try-error' in case of method dispatch failure
in the wrapped expression which to me seems not
quite correct.

Examples to reproduce the observation:

##  using functions all is well:
f <- function(x) { print(x); ret<-try(stop("forced.")); print(ret)}

f(3)
[1] 3
Error in try(stop("forced.")) : forced.
[1] "Error in try(stop(\"forced.\")) : forced.\n"
attr(,"class")
[1] "try-error"


##  using S4 classes and methods
setClass("fooBase",
         representation("VIRTUAL",
                        width      = "numeric",
                        height     = "numeric"),
         prototype(width      = 1024,
                   height     = 1024),
         validity = NULL,
         where    = .GlobalEnv,
         sealed   = TRUE,
         )

if (!isGeneric("plotObject")) {

  setGeneric("plotObject",
             def=function(x, y, ...) {
               value <- standardGeneric("plotObject")
               return(value)
             },
             where=.GlobalEnv,
             useAsDefault=TRUE
             )
}

setClass("foo",
         representation("fooBase"),
         validity = NULL,
         where    = .GlobalEnv,
         sealed   = TRUE)


plotObject.foo <- function(x, y) {
  plot(x,y)
}

setMethod("plotObject", signature=c("foo", "numeric"), plotObject.foo,
where=.GlobalEnv)


fooObject <- new("foo")
##  should fail and return object with attribute 'try-error' set
ret <- try(plotObject(fooObject, character(1)))

Error in as.list(call)[[1]] == "doTryCatch" :
        comparison (1) is possible only for atomic and list types

>is(ret)
Error in .class1(object) : object "ret" not found

which I belive is in contradiction to the documentation, where in
Details:

     The value of the expression if 'expr' is evaluated without error,
     but an invisible object of class '"try-error"' containing the
     error message if it fails.

This is crucial for our current implementation of check functions in
package RUnit.

Is this new behaviour 'as intended' and only the documentation has not
caught up?


Regards,

  Matthias





>sessionInfo()
R version 2.5.0 Under development (unstable) (2007-03-13 r40832)
i686-pc-linux-gnu

locale:
C

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

other attached packages:
rcompletion    rcompgen
    "0.1-2"     "0.1-5"

-- 
Matthias Burger                     Project Manager/ Biostatistician
Epigenomics AG    Kleine Praesidentenstr. 1    10178 Berlin, Germany
phone:+49-30-24345-371                          fax:+49-30-24345-555
http://www.epigenomics.com           matthias.burger at epigenomics.com
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