Passing class as argument in Rcpp function - rcpp

Question

I was reading the awesome Rcpp vignette on exposing c++ classes and functions using Rcpp modules. In that context, is it possible to create an Rcpp function that has a class of type Uniform as one of the arguments and that is not part of the particular module being exported? Below here is just a model of what I was thinking. The example is taken from the same vignette. The answer might be already there. It would be great if someone can point to the right place.
#include <RcppArmadillo.h>
using namespace Rcpp;
class Uniform {
public:
Uniform(double min_, double max_) :
min(min_), max(max_) {}
NumericVector draw(int n) const {
RNGScope scope;
return runif(n, min, max);
}
double min, max;
};
double uniformRange(Uniform* w) {
return w->max - w->min;
}
RCPP_MODULE(unif_module) {
class_<Uniform>("Uniform")
.constructor<double,double>()
.field("min", &Uniform::min)
.field("max", &Uniform::max)
.method("draw", &Uniform::draw)
.method("range", &uniformRange)
;
}
/// JUST AN EXAMPLE: WON'T RUN
// [[Rcpp::export]]
double test(double z, Uniform* w) {
return z + w->max ;
}

Answer 1

Following Dirk's comment, I am posting a possible solution. The idea would be to create a new instance of a class object with a pointer on it and create an external pointer that can be further passed as an argument of a function. Below here is what I have gathered from his post:
#include <RcppArmadillo.h>
using namespace Rcpp;
class Uniform {
public:
Uniform(double min_, double max_) :
min(min_), max(max_) {}
NumericVector draw(int n) const {
RNGScope scope;
return runif(n, min, max);
}
double min, max;
};
// create external pointer to a Uniform object
// [[Rcpp::export]]
XPtr<Uniform> getUniform(double min, double max) {
// create pointer to an Uniform object and
// wrap it as an external pointer
Rcpp::XPtr<Uniform> ptr(new Uniform( min, max ), true);
// return the external pointer to the R side
return ptr;
}
/// CAN RUN IT NOW:
// [[Rcpp::export]]
double test(double z, XPtr<Uniform> xp) {
double k = z + xp ->max;
return k;
}