From bernd_bischl at gmx.net  Wed Jan 13 19:25:17 2010
From: bernd_bischl at gmx.net (bernd_bischl at gmx.net)
Date: Wed, 13 Jan 2010 19:25:17 +0100 (CET)
Subject: [Rd] bug in callNextMethod (PR#14185)
Message-ID: <20100113182517.89E232830318@mail.pubhealth.ku.dk>

Hi,

there seems to be a possible bug in callNextMethod in conjunction with 
the [-operator.

Relevant info, minimal example and sessionInfo follow below:

###############################

setClass("foo", representation = representation(a = "numeric"))
setClass("bar", contains = "foo")

setMethod(
        f = "[",
        signature = signature("foo"),
        def = function(x,i,j,...,drop=TRUE) {
            cat("drop in foo-[ :", drop, "\n")
            return(1)
        }
)

setMethod(
        f = "[",
        signature = signature("bar"),
        def = function(x,i,j,...,drop=TRUE) {
            cat("drop in bar-[ :", drop, "\n")
            # we lose the value of drop here, when the call gets 
dispatched to the super method by callNextMethod
            callNextMethod()
        }
)

x <- new("foo")
x[1, drop=FALSE]
# drop in foo-[ : FALSE
y <- new("bar")
y[1, drop=FALSE]
# drop in bar-[ : FALSE
# drop in foo-[ : TRUE 

###############################

#?callNextMethod
#The statement that the method is called with the current arguments is 
more precisely as follows. Arguments that were missing in the current 
call are still missing (remember that "missing" is a valid class in a 
method signature). For a formal argument, say x, that appears in the 
original call, there is a corresponding argument in the next method call 
equivalent to x = x. In effect, this means that the next method sees the 
same actual arguments, but arguments are evaluated only once.

###############################


#S3 gets this right:

'[.foo' <- function(x, i, j, ..., drop=TRUE) {
    cat("drop in foo-[ :", drop, "\n")
}
       
'[.bar' <- function(x, i, j, ..., drop=TRUE) {
    cat("drop in bar-[ :", drop, "\n")
    NextMethod()
}

x <- 1
class(x) <- c("bar", "foo")
x[1, drop=FALSE]
# drop in bar-[ : FALSE
# drop in foo-[ : FALSE

###############################

 > sessionInfo()
R version 2.11.0 Under development (unstable) (2010-01-12 r50970)
i386-pc-mingw32

locale:
[1] LC_COLLATE=German_Germany.1252  LC_CTYPE=German_Germany.1252  
[3] LC_MONETARY=German_Germany.1252 LC_NUMERIC=C                  
[5] LC_TIME=German_Germany.1252   

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

loaded via a namespace (and not attached):
[1] tools_2.11.0



[Rd] bug in callNextMethod (PR#14185)
bernd_bischl at gmx.net