setMethodS3 fails to correctly reassign default function - r

Question

When I create s3 methods in R 2.14.1, and then call them, the s3 objects fail to execute the methods in cases where the method has the same name as functions already loaded into the workspace (i.e. base functions). Instead it calls the base function and returns an error. This example uses 'match'. I never had this problem before today. Since I last ran this code, I installed R 3.0.2, but kept my 2.14.1 version. I ran into some trouble (different trouble) with 3.0.2 due to certain packages not being up to date in CRAN, so I reverted RStudio to 2.14.1, and then this problem cropped up. Here's an example:
rm(list=ls())
library(R.oo)
this.df<-data.frame(letter=c("A","B","C"),number=1:3)
setConstructorS3("TestClass", function(DF) {
if (missing(DF)) {
data= NA
} else {
data=DF
}
extend(Object(), "TestClass",
.data=data
)
})
setMethodS3(name="match", class="TestClass", function(this,letter,number,...){
ret = rep(TRUE,nrow(this$.data))
if (!missing(number))
ret = ret & (this$.data$number %in% number)
if (!missing(letter)){
ret = ret & (this$.data$letter %in% letter)
}
return(ret)
})
setMethodS3("get_data", "TestClass", function(this,...) {
return(this$.data[this$match(...),])
})
hope<-TestClass(this.df)
hope$match()
Error in match(this, ...) : argument "table" is missing, with no default
hope$get_data()
Here's the sessionInfo() for clues:
sessionInfo()
R version 2.14.1 (2011-12-22)
Platform: i386-pc-mingw32/i386 (32-bit)
locale:
[1] LC_COLLATE=English_United States.1252 LC_CTYPE=English_United States.1252
[3] LC_MONETARY=English_United States.1252 LC_NUMERIC=C
[5] LC_TIME=English_United States.1252
attached base packages:
[1] stats graphics grDevices utils datasets methods base
other attached packages:
[1] R.oo_1.13.0 R.methodsS3_1.4.2
loaded via a namespace (and not attached):
[1] tools_2.14.1
I tried a lot of combinations of the arguments in setMethodsS3 with no luck.
How can I fix this?

Answer 1

First, I highly recommend calling S3 methods the regular way and not via the <object>$method(...) way, e.g. match(hope) instead of hope$match(). If you do that, everything works as expected.
Second, I can reproduce this issue with R 3.0.2 and R.oo 1.17.0. There appears to be some issues using the particular method name match() here, because if you instead use match2(), calling hope$match2() works as expected. I've seen similar problems when trying to create S3 methods named assign() and get(). The latter actually generates a error if tried, e.g. "Trying to use an unsafe generic method name (trust us, it is for a good reason): get". I'll add assign() and most likely match() to the list of no-no names. DETAILS: Those functions are very special in R so one should avoid using those names. This is because, if done, S3 generic functions are created for them and all calls will be dispatched via generic functions and that is not compatible with
Finally, you should really really update your R - it's literally ancient and few people will not bother trying to help you with issues unless you run the most recent stable R version (now R 3.0.2 soon to be R 3.1.0). At a minimum, you should make sure to run the latest versions of the package (your R.methodsS3 and R.oo versions are nearly 2 and 1 years old by now with important updates since).
Hope this helps