CODEWITHSUNDEEP
rfunctionclassmethods
iod
iod

Reputation: 7592

How can a method for a new class refer to the basic function it's replacing?

Suppose I want to create a method for a class I've created, but I don't have access to the code of the original function - I just want to build on top of it. Just to give a simple example that doesn't actually do anything:

x1<-1
class(x1)<-c("myclass",class(x1))
print.myclass<-function(x) {
                            x<-paste0(x,"foobar")
                            print(x)
                           }
print(x1)

If I try to run the last line, it throws the function into a loop and R eventually crashes. The solution I found was to add a line to the function that strips the new class name from x before passing it to the original function:

print.myclass<-function(x) {x<-paste0(x,"foobar"); class(x)<-class(x)[-1]; print(x)}

Is there a better/best practice way to do it?

Upvotes: 0

Views: 38

Answers (1)

Christoph
Christoph

Reputation: 7063

I think your problem is that you create an infinite loop: print(print(...).
I don't know what you want to achieve but this might be what you are looking for:

x1 <- 1
class(x1) <- c("myclass",class(x1))
print.myclass <- function(x) print.default(x)
print(x1)

Perhaps you might want to look here

BTW: I don't think your solution really solves the problem. You just delete your new class entry which causes print not to use print.myclass.

For details see Hadley

Upvotes: 2

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