Object binding between C++ and R

ObjectBindings.cpp

// About C++11: https://teuder.github.io/rcpp4everyone_en/050_c++11.html
// [[Rcpp::plugins("cpp11")]]

/* R demo
 * 
 * library(Rcpp)
 * sourceCpp("test.cpp")
 */

#include <Rcpp.h>

//// using raw pointer

struct Kr {
  int i;
  std::string s;
};

// [[Rcpp::export]]
SEXP build() {
  
  Kr *a = new Kr{42,"42"};
  
  Rcpp::XPtr<Kr> ptr(a); // TODO: check memory management
  
  return ptr;
}

// [[Rcpp::export]]
int apply(SEXP a){
  
  Rcpp::XPtr<Kr> x(a);
  int i = x->i;
  
  return i;
}
 
/* R demo
 * 
 * a <- build()
 * apply(a)
 */

/// Using S3

/* R demo
 * 
 * a <- structure(list(x=42), class = "kr")
 *       OR
 * a <- buildS3() 
 * class(a)
 * inherits(a, "kr")
 * applyS3(a)
 */

//Receiving kr() model object and calculate RMSE
// [[Rcpp::export]]
Rcpp::List buildS3() {
  Rcpp::List obj;
  obj.attr("x") = 42;
  obj.attr("class") = "kr";
  return obj;
}

// [[Rcpp::export]]
int applyS3(Rcpp::List obj) {
  if (! obj.inherits("kr")) Rcpp::stop("Input must be a km object");
  return obj.attr("x");
}


/// Using S4

// [[Rcpp::export]]
SEXP buildS4() { 
    Rcpp::S4 obj("kr");
    obj.slot("x") = 1000;
    return obj; 
}

// [[Rcpp::export]]
std::string applyS4(Rcpp::S4 obj) {
  return obj.slot("y");
}

/* R demo
 * 
 * setClass("kr", representation(x="numeric", y="character"), prototype = list(x=42, y="42"))
 * a <- buildS4()
 * applyS4(a)
 */