Right way to capture reference to member variables

[sanggs]

Hi, I am trying to understand how to use nanobind and how data ownership works.
And I have this very simple example:

my_ext.h
template <class T, int d> class Example { private: int integer; public: Example() { integer = 100; } int& getInteger(); void printClassInfo(); ~Example() {} };

my_ext.cpp
#include <nanobind/nanobind.h> #include "my_ext.h" namespace nb = nanobind; int add(int a, int b) { Example<double, 2> ex1; auto ex1b = ex1.getInteger(); ex1b = (double)a; Example<double, 2> ex2; auto ex2b = ex2.getInteger(); ex2b = (double)b; return ex1b + ex2b; } template<class T, int d> int& Example<T, d>:: getInteger() { return integer; } template<class T, int d> void Example<T, d>:: printClassInfo() { printf("Integer = %d\n", integer); } NB_MODULE(my_ext, m) { m.def("add", &add); nb::class_<Example<double, 3>>(m, "Double3Example") .def(nb::init<>()) .def("getInteger", &Example<double, 3>::getInteger, nb::rv_policy::reference_internal) .def("printClassInfo", &Example<double, 3>::printClassInfo); }

my_ext.py
from build import my_ext as example print("Create an instance of Example class") e = example.Double3Example() print("Print current class info") e.printClassInfo() print("Get the reference to a member variable") x = e.getInteger() old_x = x x = 200 print("Change value from {} to {}".format(old_x, x)) print("Print current class info") e.printClassInfo()

The output I get is
Create an instance of Example class Print current class info Integer = 100 Get the reference to a member variable Change value from 100 to 200 Print current class info Integer = 100

But shouldn't the value of integer be changed to 200? Very grateful if anyone can tell me where I am going wrong.

I apologize for the formatting issues with the code pasted above.

[wjakob]

This is all described in the documentation. Please read it.