[Rcpp-devel] wrapping a class having a method returning an object of class-type

[James Simone]

I have a C++ class that has a "clone" method which returns a distinct copy of the object.
I want to expose the clone method in R and my question is how this is best done using Rcpp?

My first attempt to expose "clone" results in a compile error since Rcpp cannot automatically handle
the returned object. Consider an example,

class Cnorm
{
public:
   Cnorm() : z(0) {}
   Cnorm(double z_) : z(z_) {}
   double operator()( double x, double y ) const { return sqrt( x*x + y*y + z*z ); }
   Cnorm clone() const { return Cnorm(z); }
private:
   double z;
};

RCPP_MODULE(mod) {
   using namespace Rcpp;
   class_<Cnorm>("Cnorm")
     .constructor<double>("constructor")
     .method("clone",&norm::clone,"clone this object")
     .method("norm",&Cnorm::operator(),"take the norm");
}

I found a solution which seems to work which involves adding
a free function. I have two questions, however,

1) Is the workaround below reasonable/best?
2) Does Rcpp properly take ownership of the new'ed Cnorm object?

  SEXP cloner(Cnorm* self) {
   Cnorm* cpy = new Cnorm;
   *cpy = self->clone();
   return  Rcpp::internal::make_new_object(cpy);
}

RCPP_MODULE(mod) {
   using namespace Rcpp;

   class_<Cnorm>("Cnorm")
     .constructor<double>("constructor")
     .method("clone",&cloner,"clone this object")
     .method("norm",&Cnorm::operator(),"take the norm");
}