diff --git a/lecture-06/adds_numbers.cpp b/lecture-06/adds_numbers.cpp
index 048c988..6943f65 100644
--- a/lecture-06/adds_numbers.cpp
+++ b/lecture-06/adds_numbers.cpp
@@ -15,13 +15,25 @@ NumericVector add_vectors(NumericVector a, NumericVector b) {
 }
 
 // [[Rcpp::export]]
-NumericVector add_vectors2(NumericVector a, NumericVector b) {
+Rcpp::NumericVector add_vectors2(
+    Rcpp::NumericVector & a,
+    const Rcpp::NumericVector & b
+) {
+
+  a = a + 1;
+
+  if (a.size() != b.size())
+    Rcpp::stop("Adding two vectors of different size!");
+
   return a + b;
 }
 
 /*** R
 add_vectors(1:5, 1:5)
-add_vectors2(1:5, 1:5)
+
+a <- 1:5
+add_vectors2(a, 1:5)
+a
 */
 
 
diff --git a/lecture-06/person-example.cpp b/lecture-06/person-example.cpp
new file mode 100644
index 0000000..e485874
--- /dev/null
+++ b/lecture-06/person-example.cpp
@@ -0,0 +1,55 @@
+#include <Rcpp.h>
+
+class Person {
+public:
+  Person(std::string name, int age) :
+  name(name), age(age) {}
+  std::string get_name() const { return name; }
+  int get_age() const { return age; }
+  void print() const {Rprintf(
+      "%s is %d years old\n", name.c_str(), age);
+  }
+
+private:
+  std::string name;
+  int age;
+};
+
+// [[Rcpp::export]]
+Rcpp::XPtr<Person> create_person(
+    std::string name, int age
+) {
+  Rcpp::XPtr<Person> person(new Person(name, age));
+
+  // Adding an attribute
+  person.attr("class") = "MyPerson";
+
+  return person;
+}
+
+// [[Rcpp::export]]
+std::string get_name(SEXP person) {
+  Rcpp::XPtr<Person> p(person);
+  return p->get_name();
+}
+
+// [[Rcpp::export]]
+int print_person(SEXP person) {
+  Rcpp::XPtr<Person> p(person);
+  p->print();
+  return 0;
+}
+
+/*** R
+
+# This is an S3 method for printing MyPerson
+print.MyPerson <- function(x) {
+  print_person(x)
+}
+
+george <- create_person("george", 123)
+
+# These two are equivalent
+george
+print(george)
+*/