The way you try to implement it would require the class B to be
wrappable. You can have a look at the Rcpp-extending vignette for how to
enable wrap for custom classes.
The vignette states that I should specialize the wrap template or
implement the operator SEXP() for my class B. Unfortunately, it does not
give any hint about how to create an appropriate SEXP from an arbitrary
object pointer. After doing some research on the internet and a look at
the Matrix package I came up with the following approach. Could
something along these lines work at all?
#include <Rdefines.h>
SEXP foo() {
B* b = new B(1);
Rcpp::XPtr<B> xptr(b);
SEXP s4_obj = PROTECT(NEW_OBJECT(MAKE_CLASS("Rcpp_B")));
SEXP slot = Rcpp::wrap(std::string("pointer"));
SET_SLOT(s4_obj, slot, xptr);
UNPROTECT(1);
return s4_obj;
}
Unfortunately, this does not work as expected. In R, the returned
variable has type "S4", which is what I want. It cannot be used, though:
Error in get(".pointer", envir = env) : Object '.pointer' not found.
Perhaps all that is missing is a way to correctly initialize the
"pointer" or ".xData" of the created object. Any hints on that?
On the other hand, since I do not really understand in detail what
happens here, the code above could also be perfect nonsense...
Best regards,
Peter
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