[R] S4 pass-by-value work-around?

[Jeffrey Spies]

Howdy all,

I have a problem that I'd like some advice/help in solving---it has to do
with R's pass-by-value system.  I understand the issue, but am wondering if
anyone has found a working solution in dealing with it for cases when one
wants to modify an object inside of a method, specifically when working with
S4.  I'm aware that R.oo is able to deal with this using S3, but I'd really
rather stick to S4.

The basics of what I would like to do are coded below:

setClass("MyMatrix",
	representation(
		parameters="matrix",
		uniqueCount="numeric"
	),
	prototype(
		parameters=matrix(numeric(0),0,0),
		uniqueCount=1	
	)
)

setGeneric("createUniqueName", function(object)
standardGeneric("createUniqueName"))

setMethod("createUniqueName", "MyMatrix", function(object){
	retval <- paste("unique_", object at uniqueCount, sep="")
	object at uniqueCount <- object at uniqueCount + 1
	return(retval)
})

x <- new("MyMatrix", parameters=matrix(0, 2, 2))
createUniqueName(x) # returns "unique_1"
x # x at uniqueCount is still 1

I understand why this is happening, but am wondering how people in the
community have dealt with it, specifically when using S4.  Any advice would
be appreciated.  Also, I am aware that this is somewhat of a silly example,
but it should allow you to see what I'm trying to accomplish.

Thank you,

Jeff.


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