>>>> "JC" == John Chambers <j...@r-project.org>
>>>> on Wed, 11 Mar 2009 09:57:43 -0700
JC> Whatever one wants for an S3 generic, it's not needed to do what,
JC> presumably, you want here.
JC>
JC> And for sure it is no excuse for S3 methods for S4 classes.
JC>
JC> Back to basics: To write S4 methods for an existing function, the clean
JC> and simple way is usually:
JC>
JC> setGeneric("time<-")
JC>
JC> If your package depends on one that has S3 methods for this function,
JC> there will be a version of the function imported into your namespace.
JC> That function will then be the default method.
JC>
JC> Presumably you want to ensure that S3 methods, for S3 classes, are still
JC> dispatched. Quite reasonable and it should follow from the call to
JC> setGeneric.
JC>
JC> If you wanted to have your own S3 methods or if you weren't willing to
JC> assume an S3 generic imported, you could do a 2-line version:
JC>
JC> R(r48103)> `time<-` <- function(x, value) UseMethod("time<-")
JC> R(r48103)> setGeneric("time<-")
JC> [1] "time<-"
JC> R(r48103)> showMethods("time<-", include = TRUE)
JC> Function: time<- (package .GlobalEnv)
JC> x="ANY"
JC> function (x, value)
JC> UseMethod("time<-")
In my opinion you example only works in '.GlobalEnv' environement, but
does not work when implemented in a package.
I wrote a small package to illustrate the problem.
## R code
oldDir <- getwd()
setwd(tempdir())
url <- "http://nic.phys.ethz.ch/~chalabi/timeProb_0.001.tar.gz";
download.file(url, "timeProb_0.001.tar.gz")
install.packages("timeProb_0.001.tar.gz", repos = NULL)
# you also need to install another package which uses `time<-`.
# for example zoo
if(!require(zoo))
install.packages("zoo")
# Now we quit and start a new R session
setwd(oldDir)
q()
# new R
# we first load timeProb
library(timeProb)
# and then run the demo
demo(timeProb)
# now we quit and start again a new session
q()
# new R
# but now we first load zoo and after timeProb
library(zoo)
library(timeProb)
# and run again the demo
demo(timeProb)
## end R code
As far as I understand it, two packages can not coexist if one of
them defines an S3 generic and the other one defines an S4 generic
with the same name.
Or am I missing an option when defining the S4 generic?
JC>
JC> As a postscript, here is the current plan, not yet committed, pending
JC> some more testing:
JC> - the bad methods will be allowed
JC> - warnings when a class is defined with such methods for a superclass
JC> - probably some other warnings, but not for an ordinary call to the
JC> method (it's the MISSING calls to the method that are the disaster).
JC>
Thanks for giving more information concerning the current plan.
JC> More later,
JC> John
JC>
regards,
Yohan
--
PhD student
Swiss Federal Institute of Technology
Zurich
www.ethz.ch
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