Trampoline usage with interface class

[maartentamboer]

Hi, I'm running into an issue when trying to bind an interface class (pure virtuals) that has a protected destructor.
When running on the debug build the program aborts and shows the following error in the console:
Critical nanobind error: nanobind::detail::inst_dealloc("test_compiled.CustomPureVirtualInterface"): attempted to call the destructor of a non-destructible type!

class IPureVirtualInterface
{
public:
  virtual void Set(bool value) = 0;
protected:
  virtual ~IPureVirtualInterface() = default;
};

class PyPureVirtualInterface : public IPureVirtualInterface
{
public:
  NB_TRAMPOLINE(IPureVirtualInterface, 1);
  void Set(bool Value) override { NB_OVERRIDE_PURE(Set, Value); }
};

NB_MODULE(_core, m)
{
  m.def("test_param", [](IPureVirtualInterface& i) {
    i.Set(true);
  });

  nb::class_<IPureVirtualInterface, PyPureVirtualInterface>(m, "IPureVirtualInterface")
    .def(nb::init<>())
    .def("Set", &IPureVirtualInterface::Set, "Set a value");
}

import package_name._core as m

class CustomPureVirtualInterface(m.IPureVirtualInterface):
    def Set(self, arg: bool) -> None:
        print(f"PY: Set called with value: {arg}")


def test_interface():
    x = CustomPureVirtualInterface()
    m.test_param(x)

I've tried adding a destructor to PyPureVirtualInterface (~PyPureVirtualInterface() = default;) but that does not resolve it.

If this is not possible to achieve, it is acceptable to forego the trampoline, since it is a nice to have in my usecase. But then my followup will be how to bind that interface class, since I could not find any details on Non-public destructors like mentioned in pybind11 https://pybind11.readthedocs.io/en/stable/advanced/classes.html#non-public-destructors

[wjakob]

You need to un-protect the destructor of the parent class. The type of code you are trying to bind is not supported by nanobind.

[maartentamboer]

Thanks for the quick reply! I'll try to figure something out with an extra wrapper class in between then since the interface itself is unfortunately not changeable in my use case.