S3 Class Names: What's Allowed?

Question

Are there any restrictions on the names of S3 classes? For instance, are spaces allowed in the name? I see that data frames have a class of "data.frame" not "data frame". If there is not a formal restriction, are there potential problems with having spaces in the name? I just don't run into anything other than the basic modes so I'm sure those of you with more experience will know.

Answer 1

Doesn't look there are many restrictions at all. Check out this monstrosity:

`plot.44 !@#$%^&` <- function(x) {
     plot(rnorm(x), pch=16, col="red",
          main = "But why would you want to do this??")
}

dat <- 55
class(dat) <- "44 !@#$%^&"
plot(dat)

One reason not to put spaces into a class name is that it makes it a bit trickier to directly call methods for that class.

plot.44 !@#$%^&(100)   # This doesn't work 

`plot.44 !@#$%^&`(100) # You have to do this instead

Answer 2

Spaces are allowed:

test = 1
class( test ) = c( class( test ) , "My Class" )

Not sure about other restrictions or consequences of having special characters in class names. Certainly having spaces/special characters in class names is not conventional (not just R, but other languages). I suggest avoiding that.