[Rd] [External] R C api for 'inherits' S3 and S4 objects

[Jan Gorecki]

Thank you all for your valuable comments.
Best,
Jan

On Fri, Nov 1, 2019 at 8:15 PM Tierney, Luke <luke-tierney using uiowa.edu> wrote:
>
> On Fri, 1 Nov 2019, Jan Gorecki wrote:
>
> > Thank you Luke.
> > That is why I don't use Rf_inherits but INHERITS which does not
> > allocate, provided in the email body.
>
> Your definition can allocate because STING_ELT can allocate.
> getAttrib can GC in general. Currently it would not GC or allocate in
> this case, but this could change.
>
> You can't assume thread-safety for calls into the R API, or any API
> for that matter, unless they are documented to be thread-safe.
>
> You would be better off using Rf_inherits as it does not make the
> assumption that you can use pointer comparisons to check for identical
> strings.  CHARSXPs are almost always cached but they are not
> guaranteed to be, and the caching strategy might change in the future.
>
> Best,
>
> luke
>
> > I cannot do similarly for S4 classes, thus asking for some API for that.
> >
> > On Fri, Nov 1, 2019 at 5:56 PM Tierney, Luke <luke-tierney using uiowa.edu> wrote:
> >>
> >> On Fri, 1 Nov 2019, Jan Gorecki wrote:
> >>
> >>> Dear R developers,
> >>>
> >>> Motivated by discussion about checking inheritance of S3 and S4
> >>> objects (in head matrix/array topic) I would light to shed some light
> >>> on a minor gap about that matter in R C API.
> >>> Currently we are able to check inheritance for S3 class objects from C
> >>> in a robust way (no allocation, thread safe). This is unfortunately
> >>
> >> Your premise is not correct. Rf_inherits will not GC but it can
> >> allocate and is not thread safe.
> >>
> >> Best,
> >>
> >> luke
> >>
> >>> not possible for S4 classes. I would kindly request new function in R
> >>> C api so it can be achieved for S4 classes with no risk of allocation.
> >>> For reference mentioned functions below. Thank you.
> >>> Jan Gorecki
> >>>
> >>> // S3 inheritance
> >>> bool INHERITS(SEXP x, SEXP char_) {
> >>>  SEXP klass;
> >>>  if (isString(klass = getAttrib(x, R_ClassSymbol))) {
> >>>    for (int i=0; i<LENGTH(klass); i++) {
> >>>      if (STRING_ELT(klass, i) == char_) return true;
> >>>    }
> >>>  }
> >>>  return false;
> >>> }
> >>> // S4 inheritance
> >>> bool Rinherits(SEXP x, SEXP char_) {
> >>>  SEXP vec = PROTECT(ScalarString(char_));
> >>>  SEXP call = PROTECT(lang3(sym_inherits, x, vec));
> >>>  bool ans = LOGICAL(eval(call, R_GlobalEnv))[0]==1;
> >>>  UNPROTECT(2);
> >>>  return ans;
> >>> }
> >>>
> >>> ______________________________________________
> >>> R-devel using r-project.org mailing list
> >>> https://stat.ethz.ch/mailman/listinfo/r-devel
> >>>
> >>
> >> --
> >> Luke Tierney
> >> Ralph E. Wareham Professor of Mathematical Sciences
> >> University of Iowa                  Phone:             319-335-3386
> >> Department of Statistics and        Fax:               319-335-3017
> >>     Actuarial Science
> >> 241 Schaeffer Hall                  email:   luke-tierney using uiowa.edu
> >> Iowa City, IA 52242                 WWW:  http://www.stat.uiowa.edu
> >
>
> --
> Luke Tierney
> Ralph E. Wareham Professor of Mathematical Sciences
> University of Iowa                  Phone:             319-335-3386
> Department of Statistics and        Fax:               319-335-3017
>     Actuarial Science
> 241 Schaeffer Hall                  email:   luke-tierney using uiowa.edu
> Iowa City, IA 52242                 WWW:  http://www.stat.uiowa.edu