>From an example in
>http://www.uni-muenster.de/ZIV.BennoSueselbeck/s-html/helpfiles/nargs.html ,
>number of arguments in '...' can be obtained by
(function(...)nargs())(...) .
I now realize that sys.call() doesn't expand '...' when the function is called
with '...'. It just returns the call as is. If 'stopifnot' uses sys.call()
instead of match.call() , the following example behaves improperly:
g <- function(...) stopifnot(...)
g(TRUE, FALSE)
--------------------------------------------
On Thu, 18/5/17, Martin Maechler <maech...@stat.math.ethz.ch> wrote:
Subject: Re: [Rd] stopifnot() does not stop at first non-TRUE argument
Cc: r-devel@r-project.org
Date: Thursday, 18 May, 2017, 3:03 PM
>>>>> Suharto Anggono Suharto Anggono via R-devel <r-devel at r-project.org>
>>>>> on Tue, 16 May 2017 16:37:45 +0000 writes:
> switch(i, ...)
> extracts 'i'-th argument in '...'. It is like
> eval(as.name(paste0("..", i))) .
Yes, that's neat.
It is only almost the same: in the case of illegal 'i'
the switch() version returns
invisible(NULL)
whereas the version we'd want should signal an error, typically
the same error message as
> t2 <- function(...) ..2
> t2(1)
Error in t2(1) (from #1) : the ... list does not contain 2 elements
>
> Just mentioning other things:
> - For 'n',
> n <- nargs()
> can be used.
I know .. [in this case, where '...' is the only formal argument of the
function]
> - sys.call() can be used in place of match.call() .
Hmm... in many cases, yes.... notably, as we do *not* want the
argument names here, I think you are right.
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