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Named class vector

2 messages · Duncan Murdoch, Kurt Hornik

Original
Duncan Murdoch
# 
The source to the noquote() function looks like this:

noquote <- function(obj, right = FALSE) {
     ## constructor for a useful "minor" class
     if(!inherits(obj,"noquote"))
         class(obj) <- c(attr(obj, "class"),
                         if(right) c(right = "noquote") else "noquote")
     obj
}

Notice what happens with right = TRUE:

 > x <- noquote("a", right = TRUE)
 > x
[1] a
 > class(x)
     right
"noquote"

The class vector for x is named.  The print method pays attention to the 
name, so we get different behaviour for a class of "noquote" and a class 
of c(right = "noquote").

I had never noticed a named class vector before, and it raised some 
questions for me:

- Is this used anywhere else?
- Are names preserved in all the operations normally done on a class 
vector?  (As far as I can see they are, but maybe I've missed something.)
- Is it a good idea to encode a string value worth of information in the 
name, rather than setting the class to something like c("noquote", 
"right") instead?

Comments would be welcome.

Duncan Murdoch
Kurt Hornik
# 
Not that I'd be aware of: I think MMae is the expert here.
My preference would be to have unnamed class vectors, so that the names
could perhaps eventually be used to store the name of the package which
owns the class.  For noquote, I guess you'd want something like

  c("noquote_right", "noquote")

Best
-k