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:
Foo <- function(value=0) {
this <- list(
value = value
)
class(this) <- "Foo";
return(this);
}
set <- function(object, value) {
this <- .Alias(object);
this$value <- value;
return (invisible());
}
get <- function(object) {
return (object$value);
}
a <- Foo();
b <- Foo(10);
cat("a =", get(a), "\n"); # a = 0
cat("b =", get(b), "\n"); # b = 10
set(a, 10);
set(b, 20);
cat("a =", get(a), "\n"); # a = 10
cat("b =", get(b), "\n"); # b = 20
Have a nice day
Henrik Bengtsson
PhD Student in Statistics
Lund University & UC Berkeley
henrikb at braju.com
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"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 -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-help 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-help-request at stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._