[Rcpp-devel] Rcpp modules and return_value_policy for exposed C++ member functions

[Claymore Marshall]

I want to expose to R several C++ classes from a library with Rcpp
modules.  I'm trying to imitate a similar set of Python modules that were
made for the same library.

In Boost.Python, with .def it is possible to specify the
return_value_policy.  Is it also possible to do this in a straight forward
way with Rcpp modules when exposing C++ class methods?

The following simplified example illustrates a problem I face with using
Rcpp modules.  When R deletes 'res', R crashes shortly after (a segfault?).


With a Python module, this kind of problem apparently doesn't come about by
setting in .def the following:
return_value_policy<reference_existing_object>()

Is there an easy way to get around this problem with Rcpp modules with
minimal code?

#include <Rcpp.h>
using namespace Rcpp;

class A {

  public:

    A(int x_) : x(x_){}

    int x;
};

class B {

  public:
    B():m_A(10) {}

    A get_an_A(){
      A an_A(3);
      return an_A;
    }
    A * get_member_A() { return & m_A; }

  private:
    A m_A;
};

RCPP_EXPOSED_CLASS(A)
RCPP_EXPOSED_CLASS(B)

RCPP_MODULE(AB_mod){
  using namespace Rcpp ;
  class_<A>("A")
   .constructor<int>()
   .field("x", &A::x)
  ;
  class_<B>("B")
   .constructor()
   .method("get_an_A",&B::get_an_A)
   .method("get_member_A", &B::get_member_A)
  ;
}



------------------------

R code:

A_eg <- new(A, 10)
B_eg <- new(B)

res <- B_eg$get_member_A()

rm(res)
# R crashes shortly after running further commands ...
# How can this error be prevented?
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