Error using Rcpp::Nullable with RcppArmadillo types

Question

I\'m using RcppArmadillo in my R package and I would like to use the Rcpp::Nullable in the parameter list.

NumericVector d_snb(NumericVector& x,
                 


        

Answer 1

Yes, Rcpp::Nullable<> works only around SEXP-based Rcpp types.

So you have to do the two-step procedure you found. But I think you can do one simpler: arma::mat test = Rcpp::as<arma::mat>(size_param);

Here is a complete example which compiles (but does 'nothing'):

#include <RcppArmadillo.h>
// [[Rcpp::depends(RcppArmadillo)]]

// [[Rcpp::export]]
void d_snb(Rcpp::NumericVector& x,
           Rcpp::Nullable<Rcpp::NumericVector> size_param = R_NilValue) {

  if (size_param.isNotNull()) {
    arma::vec test = Rcpp::as<arma::vec>(size_param);
    test.print("vector");
  }
  Rcpp::Rcout << x << std::endl;

}

And a quick demo:

R> sourceCpp("/tmp/so44102346.cpp")
R> d_snb(c(1,2,3))
1 2 3
R> d_snb(c(1,2,3), c(4,5,6))
vector
   4.0000
   5.0000
   6.0000
1 2 3
R>