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

Thank you Luke.
That is why I don't use Rf_inherits but INHERITS which does not
allocate, provided in the email body.
I cannot do similarly for S4 classes, thus asking for some API for that.
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;
}

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Luke Tierney
Ralph E. Wareham Professor of Mathematical Sciences
University of Iowa                  Phone:             319-335-3386
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    Actuarial Science
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[External] R C api for 'inherits' S3 and S4 objects

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