[Rd] Suggestion: mkString(NULL) should be NA

[Michael Lawrence]

On Wed, May 25, 2016 at 4:23 AM, Jeroen Ooms <jeroen.ooms at stat.ucla.edu>
wrote:

> On Wed, May 25, 2016 at 12:31 PM, Martin Maechler
> <maechler at stat.math.ethz.ch> wrote:
> > Better than segfaulting, yes, but really agree with Bill (and
> > Gabe), also for Rf_mkChar(NULL):
> > I think both functions should give an error in such a case
> > rather than returning NA_character_
> >
> > It is an accident of some kind if they got NULL, no?
>
> Not necessarily. A char* of NULL can be a string which is not
> initiated or simply unavailable due to configuration.
>
> The example from my original email was in curl package which exposes
> the version string of libz that was used to build libcurl:
>
>   mkString(data->libz_version)
>
> This worked on all platforms that I tested. However a user found that
> if libcurl was configured --without-libz (which is uncommon) the
> libz_version string does not get set by libcurl and is always NULL. I
> had not foreseen this and it would lead to a segfault.
>
> I think making mkString() return NA for null strings lead to the most
> robust behavior. Raising an exception seems a little harsh to me, as
> there is no way the user would be able to recover from this, and there
> might not be an actual problem at all.
>
>
Robust in the sense of no error being thrown, but perhaps only correct by
accident. NULL is not a valid C string --- should functions always return
NA on invalid input? As Gabe mentions, in the cited use case, it's not
clear whether the appropriate value is NA, "", or something else entirely.
Generalization seems risky at this point.


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