[Rd] surprising behaviour of names<-

[William Dunlap]

Would it make anyone any happier if the manual said
that the replacement functions should not be called
in the form
   xNew <- `func<-` (xOld, value)
and should only be used as
   func(xToBeChanged) <- value
? 

The explanation
      names(x) <- c("a","b")
  is equivalent to
      '*tmp*' <- x
      x <- "names<-"('*tmp*', value=c("a","b"))
could also be extended a bit, adding a line like
      rm(`*tmp*`)
Those 3 lines should be considered an atomic operation:
the value that `*tmp*` or `x` may have or what is
in the symbol table at various points in that sequence 
is not defined.  (Letting details be explicitly undefined
is important: it gives developers room to improve the
efficiency of the interpreter and tells users where not to go.) 


Bill Dunlap
TIBCO Software Inc - Spotfire Division
wdunlap tibco.com  

> -----Original Message-----
> From: r-devel-bounces at r-project.org 
> [mailto:r-devel-bounces at r-project.org] On Behalf Of Wacek Kusnierczyk
> Sent: Friday, March 13, 2009 11:42 AM
> To: Berwin A Turlach
> Cc: r-devel at r-project.org List
> Subject: Re: [Rd] surprising behaviour of names<-
> ... blah blah blah
> >>     x = 1
> >>     tmp = x
> >>     x = 'names<-'(tmp, 'foo')
> >>     names(tmp)
> >>     # NULL