[R] S4 class slot name 'names' is not allowed
slacey at umich.edu
Thu Apr 13 13:34:04 CEST 2006
Thanks! I'll use name for now.
From: Martin Maechler [mailto:maechler at stat.math.ethz.ch]
Sent: Thursday, April 13, 2006 3:11 AM
To: Steven Lacey
Cc: R-bugs at stat.math.ethz.ch; r-help at stat.math.ethz.ch
Subject: S4 class slot name 'names' is not allowed
>>>>> "SteveL" == Steven Lacey <slacey at umich.edu>
>>>>> on Wed, 12 Apr 2006 19:06:52 -0400 writes:
SteveL> Hi, Why doesn't this work?
setClass("tests", representation(names = "character"))
tmp <- new("tests"); tmp at names <- "a"
SteveL> Error in "slot<-"(object, name, TRUE, value) :
SteveL> 'names' attribute  must be the same length as the vector 
SteveL> Why does this work (replace names with name)?
tmp <- new("test"); tmp at name <- "a"
SteveL> I looked at the help for setClass, representation,
SteveL> and slot and found no restriction on the slot names
SteveL> other than that they "be any non-empty string, but
SteveL> if the name is not made up of letters, numbers, and
SteveL> '"."', it needs to be quoted".
Hah, you got us!
This *is* a bug - at least in the documentation ===> This goes to R-bugs as
It's because of the current *implementation* of S4-classed objects in R [as
an empty list with a list of unusual attributes]
-- and because 'names' (and also, e.g., 'dimnames')
are attributes in R with a very special treatment - in many places.
I haven't delved into the internal code, but I know that this problem will
go away ``as soon as'' the internal representation of S4-classed objects is
replaced -- something that has been planned for a while and "just did not
Martin Maechler, ETH Zurich
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