Hi,
When a method is not defined for an object, you
expect to get an error. But this is not the case for
"names<-". You can use "names<-" on any S4 object: it
will remain silent, giving you the impression that it
actually did something:
setClass("A", representation(vals="numeric"))
setMethod("names", "A", function(x) names(x...@vals))
> vals <- 8:2
> names(vals) <- letters[1:7]
> a <- new("A", vals=vals)
> names(a)
[1] "a" "b" "c" "d" "e" "f" "g"
> names(a) <- LETTERS[1:7] # no error
> names(a)
[1] "a" "b" "c" "d" "e" "f" "g" # nothing has changed
Shouldn't "names<-" return an error like "[" or "[<-" do
in such situation?
> a[2]
Error in a[2] : object of type 'S4' is not subsettable
> a[2] <- 55
Error in a[2] <- 55 : object of type 'S4' is not subsettable
That would make it more convenient to implement classes where
instances have immutable names. For now I need to use the
following workaround:
setReplaceMethod("names", "A", function(x, value) stop("cannot set
my names"))
> names(a) <- LETTERS[1:7]
Error in `names<-`(`*tmp*`, value = c("A", "B", "C", "D", "E", "F", "G" :
cannot set my names
but that shouldn't be necessary.
Thanks!
H.
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