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

From: Henrik Bengtsson <hb_at_stat.berkeley.edu>
Date: Thu, 19 Jun 2008 11:08:46 -0700

Quick comment. Use an environment to hold your "fields" and then pass around the environment variable. Any modification to variables inside the environment done from anywhere (inside/outside functions) will be persistent. Then wrap this up in a class structure, overload, say, '$', '[[', '$<-', '[[<-' to get() and assign() to your object and you have the first seed of what is done in R.oo.

Note that '$' are '$<-' indeed available for environments. However, it is not recommended to extend the environment class itself. Instead you should wrap the environment up in a list and work from that. Search the R mailing list archives for issues you would/will face if you inherit from environment.

My $.02

Henrik
(R.oo author)

On Wed, Jun 18, 2008 at 10:26 PM, Jeffrey Spies <jspies2008_at_gmail.com> wrote:
>
> 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.
>
>
> --
> View this message in context: http://www.nabble.com/S4-pass-by-value-work-around--tp17997553p17997553.html
> Sent from the R help mailing list archive at Nabble.com.
>
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>



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https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Thu 19 Jun 2008 - 18:58:23 GMT

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