[Rcpp-devel] Create an instance of a reference class for a C++ class exported as a module from within C++?

Christian Gunning xian at unm.edu
Mon Jun 6 06:09:05 CEST 2011

> At the moment the only way i see is to make an R call to "new" and construct the object this way...

>> Many of the methods for this class return other members of this class.
>> Can I create a new instance of the reference class in R from within
>> the module?  I'm sure it is possible, I'm just wondering if there is
>> an easy way to do this without duplicating large chunks of the code in
>> Rcpp/src/Module.cpp.  Can i somehow clone the SEXP representing the
>> current instance then swap the external pointer to the C++ object?

I played with this a little more, and the following works fine.
Nothing striking here. The part I don't understand is, can you employ
the SEXP returned by spawn() as an instance of Bar, or are you then
stuck with the R interface to Bar?


## in R
Rcpp.package.skeleton('testmod', module=T)

//in testmod/src/rcpp_module.cpp

#include <Rcpp.h>
using namespace Rcpp;
class Bar {
    Bar()  {}
    void set(int state_) { this->state = state_; }
    int get() { return state; }

    SEXP spawn() {
        Environment meth("package:methods");
        Function Rnew = meth["new"];
        Function Rget("get");
        SEXP NewObj( Rnew(Rget("Bar")) );
        return NewObj;
    int  state;

## in R
bb = new(Bar); bb$set(3)
cc = bb$spawn();  cc$set(4)
bb$get(); cc$get()

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