bad_cast after updating nanobind and dolfinx

[497e0bdf29873]

I just updated dolfinx and everything else in my conda environment. They’re now 0.10.0 and 2.9.2, respectively. Previous versions were installed this summer; not sure which one exactly they were. With those previous versions, the following C++ code, applied to the _cpp_object inside the Python-side dolfinx Function, used to work:

    typedef Function<double> Function_f64;

    const Function_f64* cast_Function_f64(const PyObject* obj) {
        auto handle = nanobind::handle(obj);
        return nanobind::cast<const Function_f64*>(handle);
    }

Now, after the update, it throws std::bad_cast.

Anybody have an idea what has changed? Is there any other way to get the C++ object pointer to use in my code.

The following code, added to the above function, confirms that the Python-side obj is a Function_float64, which, AFAIK, should be the nanobind-wrapped C++ side Function<double>.

        const char* cstr = PyUnicode_AsUTF8(PyType_GetName(obj->ob_type));
        std::cout << cstr << std::endl;

I’m using direct PyObjects here, because my own bindings are Python ← pyo3 → Rust – cxx → C++, with the main part of my own abstract code written in Rust, and some fenics-extensibility in Python. But I also need some higher performance parts that need access to the C++ side of fenics-dolfinx.

[497e0bdf29873]

Downgrading to nanobind 2.8.0 and dolfinx 0.9.0 from conda-forge, the problem disappears. So what happened between those versions?