Message-ID: <x2r8zqchbw.fsf@blueberry.kubism.ku.dk>
Date: 2001-03-22T08:56:35Z
From: Peter Dalgaard
Subject: Call by reference: Was: Object orientation?
In-Reply-To: "Henrik Bengtsson"'s message of "Wed, 21 Mar 2001 20:10:05 -0800"
"Henrik Bengtsson" <henrikb at braju.com> writes:
> To reply to Yves Gauvreau question (Jan 24, 2001) about how to set values
> within function, it is possible to do without without using the "<<-"
> assignment operator or other nasty tricks. I had the same problem and I did
> a nasty workaround two weeks ago implementing the functionality of reference
> variables, but today I "ran into" the [R] help page for ".Alias". With
> .Alias one can immitate call by reference! Here is an example that shows how
> it works:
.....
> set <- function(object, value) {
> this <- .Alias(object);
> this$value <- value;
> return (invisible());
> }
It may work, but I wouldn't think it is documented to do so and could
easily get blown away by an internal change (and *I'm* not going to put
checks in to ensure that it keeps working)!
If you really must do this kind of thing, try coding along the lines
of
set<-function(object,value)
eval.parent(substitute(object$value<-value))
Or use assign(), or even "<<-", at least that is well-defined. It can't
get nastier than .Alias.
--
O__ ---- Peter Dalgaard Blegdamsvej 3
c/ /'_ --- Dept. of Biostatistics 2200 Cph. N
(*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk) FAX: (+45) 35327907
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