[Rcpp-devel] Passing XPtr between functions

Many thanks Krzysztof, your suggestion works.  I can explicitly create a
'new' arma::mat object and pass the resulting XPtr between functions.  I
will work on making everything prettier and document for a submission to
Rcpp Gallery unless someone is aware of one that already exists that I
somehow overlooked.

// [[Rcpp::export]]
SEXP testXptr(NumericMatrix A)
{
    arma::mat *armaMat = new arma::mat(A.begin(),A.rows(), A.cols(), false);
    XPtr<arma::mat> pMat(armaMat);
    return(pMat);
}

// [[Rcpp::export]]
void testReturn(SEXP ptrA, int nr, int nc)
{
    XPtr<arma::mat> ptrB(ptrA);
    arma::mat B = arma::mat( (double *) ptrB->memptr(),
          nr,
          nc,
          false);
    B.print("copied matrix");
}