Can an object reference itself?

Mon, Jan 18, 2010 10:50 AM

Hadley,

thanks for your comment. What you're saying is true, of course, and possibly
I did not really chose the best header to describe the actual issue I was
addressing. However, in the help archive I found something that gets me what
I want (calling a certain "slot function" without having to specify
arguments at calling time). I adapted it to my situation and maybe it's of
interest for someone facing a similar problem.

setClass(
	Class="Testclass",
	representation=representation(
		env="environment",
		data="function"
	)
)

data.fun <- function(env) get("actual.data", env=env)

setMethod(
	f="initialize", 
	signature=signature("Testclass"), 
	definition=function(
		.Object, 
		actual.data=NULL, 
		...
	) {
	     env 			<- new.env(parent=emptyenv())
	     env$actual.data 	<- actual.data
		 
		data.fun.wrapper <- function() data.fun(env)
		 
	     callNextMethod(.Object, env=env, data=data.fun.wrapper, ...)
 	}
)

obj <- new("Testclass", actual.data=1:10)
obj at data()
obj at env$actual.data	<- 1:5
obj at data()

obj.mod <- new("Testclass")
obj.mod at env$actual.data	<- "horst"
obj.mod at data()

Loading an object from harddrive could be implemented in a similar way by
putting the path-filename-combination in "obj at env" and adapting the function
"data.fun()" accordingly.

Putting "data.fun()" into the wrapper "data.fun.wrapper()" allows for
changes in "data.fun()" without having to re-source the method for
"initialize()" and to reassign "obj" each time.

Regards,
Janko

-----Urspr?ngliche Nachricht-----
Von: hadley wickham [mailto:h.wickham at gmail.com]
Gesendet: Freitag, 15. Januar 2010 19:35
An: Janko Thyson
Cc: r-help at r-project.org
Betreff: Re: [R] Can an object reference itself?

On Fri, Jan 15, 2010 at 5:30 PM, Janko Thyson
<janko.thyson at ku-eichstaett.de> wrote:

Dear List,

I am not really familiar with any other language than R, but I?ve

heard that

in other languages there is something called ?self referencing?.

Here?s what I?m trying to get an answer for:
Suppose there is a function that takes as its input a value of a slot

of an

S4 object. The function itself is stored in another slot of the SAME

S4

object. Is it then possible to have the function automatically

?recognize?

the name of the object in which slot it is placed via some sort of

?self

referencing? of the S4 object (to avoid having to explicitly state

the

required function argument for different S4 object instances with

different

names)?

I hope the following code snippets will give you an idea what I?m

trying to

do:

obj.for.slot <- data.frame(a=1); obj.for.slot <- data.frame(a=100)
save(obj.for.slot, file="C:/obj.1.for.slot.Rdata");

save(obj.for.slot,

file="C:/obj.2.for.slot.Rdata")

slotfun <- function(obj.name)
{
? ? ? ?file.fqn.char <- paste("file.fqn <- ", obj.name, "@file.fqn",
sep="")
? ? ? ?eval(parse(text=file.fqn.char))
? ? ? ?load(file=file.fqn)
? ? ? ?return(obj.for.slot)
}

setClass(
? ? ? ?Class="Testclass",
? ? ? ?representation=representation(
? ? ? ? ? ? ? ?file.fqn="character",
? ? ? ? ? ? ? ?data="function"
? ? ? ?),
? ? ? ?prototype=prototype(
? ? ? ? ? ? ? ?file.fqn="blabla",
? ? ? ? ? ? ? ?data=slotfun
? ? ? ?)
)

test ? ? ? ? ? ?<- new("Testclass")
test.mod ? ? ? ?<- new("Testclass")


test at file.fqn ? ? ? ? ? <- "C:/obj.1.for.slot.Rdata"
test.mod at file.fqn ? ? ? <- "C:/obj.2.for.slot.Rdata"

test at data(obj.name="test")
test.mod at data(obj.name="test.mod")

An object does not have a unique name.  What would happen in the
following situations?

t3 <- test.mod
tests <- list(
  test,
  test.mod
)

Hadley

--
http://had.co.nz/

Can an object reference itself?

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