The class attribute on an environment seems buggy (PR#2159)
Peter Dalgaard BSA wrote:
John Chambers <jmc@research.bell-labs.com> writes:
Would there be a problem with a "fix" in which the environment was left unduplicated, but environments with attributes are "duplicated" by creating a copy of the attribute list, but with the copy still pointing to the same environment? If that is not possible, it would be good to have another datatype that had roughly those properties. Otherwise, it's difficult to build on this datatype in designing new classes. (The same issue applies to other types, such as external pointers.)
I've been wrapping such environments in lists, as in
tclVar
function (init = "")
{
n <- evalq(TclVarCount <- TclVarCount + 1, .TkRoot$env)
name <- paste("RTcl", n, sep = "")
l <- list(env = new.env())
assign(name, NULL, envir = l$env)
reg.finalizer(l$env, function(env) tkcmd("unset", ls(env)))
class(l) <- "tclVar"
tclvalue(l) <- init
l
}
where the list(env = new.env()) construct is to avoid sticking a class
directly on "env".
What you're suggesting would seem to have the same effect, i.e. the
environment gets effectively embedded in a structure on which you can
set attributes. It does sound like it could work.
For class-related work, embedding in a list (yes, I do that too) has somewhat the wrong message, because now the object appears to extend "list", whereas the intended model is that it extends "environment". The distinction isn't all academic, because one would like to avoid list-style computations for "[", etc, which are pretty much guaranteed to cause trouble.
I'm just a little worried whether it would be clear enough to the end user what is going on, or whether we'd just be compounding problems of duplications that don't duplicate...
My personal need is for something that acts as a reference (aka database, object table, etc.) The understanding is that setting named elements in this object works as for a reference--all copies see the changes. If the object can otherwise behave in standard "S language" semantics, programming will be more straightforward. For now, I use a list containing an environment, but eventually something more direct will likely be needed.
BTW, this was never a bug...
OK, but as Henrik's mail suggested, users get unpleasant suprises from trying to treat environments as ordinary objects.
-- O__ ---- Peter Dalgaard Blegdamsvej 3 c/ /'_ --- Dept. of Biostatistics 2200 Cph. N (*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918 ~~~~~~~~~~ - (p.dalgaard@biostat.ku.dk) FAX: (+45) 35327907
John M. Chambers jmc@bell-labs.com Bell Labs, Lucent Technologies office: (908)582-2681 700 Mountain Avenue, Room 2C-282 fax: (908)582-3340 Murray Hill, NJ 07974 web: http://www.cs.bell-labs.com/~jmc -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-devel mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-devel-request@stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._