>>>>> "Ross" == Ross Boylan <[EMAIL PROTECTED]>
>>>>> on Fri, 03 Jun 2005 17:04:08 -0700 writes:
Ross> I defined an S4 class with a slot i. Then I wrote a regular function
Ross> that attempted to increment i.
Ross> This didn't work, apparently because of the general rule that a
function
Ross> can't change the values of its arguments outside the function. I
gather
Ross> there are ways around it, but the Green book admonishes "cheating on
the
Ross> S evaluation model is to be avoided" (p. 190).
Ross> Thinking that class methods needed to an exception to this rule, I
then
Ross> tried setMethod with the function I had written. However, when I
called
Ross> the function I got
>> setMethod("nextPath", "CompletePathMaker", nextPath)
Ross> Creating a new generic function for 'nextPath' in '.GlobalEnv'
Ross> [1] "nextPath"
>> nextPath(pm)
Ross> Error: protect(): protection stack overflow
Ross> I can change the value of the slot interactively, so the problem does
Ross> not appear to be that the slots are considered off-limits.
Ross> What do I need to do to update slot values?
Ross> Here are some possibly relevant code fragments
Ross> setClass("CompletePathMaker",
Ross> representation(i="integer",
Ross> timeOffset="numeric", # to avoid 0's
Ross> truePaths="TruePaths")
Ross> )
Ross> nextPath <- function(pm){ #pm is a CompletePathMaker
Ross> [EMAIL PROTECTED] <- [EMAIL PROTECTED](1)
Ross> [etc]
If your nextPath function has 'pm' as its last statement it
will return the updated object, and if you call it
as
mypm <- nextPath(mypm)
you are
1) updating mypm
2) in a proper S way (i.e. no cheating).
Regards,
Martin
Ross> I'm trying to make the class behave like an iterator, with i keeping
Ross> track of its location. I'm sure there are more R'ish ways to go, but
Ross> I'm also pretty sure I'm going to want to be able to update slots.
Ross> Thanks.
Ross> Ross Boylan
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