[Python] Overriding C++ class virtual methods in Pybind11 with trampoline class - but still...

I'm implementing a Pybind11 module, and I'm exposing a C++ class to Python that it's meant to be subclassed. I'm following what's described in here (https://pybind11.readthedocs.io/en/stable/advanced/classes.html) and below is the code for the C++ base and trampoline class.

class CollisionResponse {
public:
CollisionResponse() : _tag1(0), _tag2(1) {}
virtual ~CollisionResponse() = default;
virtual void onStart() const {
std::cout << "base called\n";
}

int getTag1() const;
int getTag2() const;
protected:
int _tag1;
int _tag2;
};


class PyCollisionResponse : public CollisionResponse {
public:
using CollisionResponse::CollisionResponse;

void onStart() const override {

PYBIND11_OVERRIDE(
void, // Return type
CollisionResponse, // Parent class
onStart // Name of function in C++
);

}
};


Below is how I expose the class to Python:

py::class_<CollisionResponse, PyCollisionResponse,
std::shared_ptr<CollisionResponse>>(m, "CollisionResponse")
.def(py::init<>())
.def("onStart", &CollisionResponse:nStart);


Now I have a C++ object which holds a map of CollisionResponse objects, that are passed from Python via the addResponse method:

class CollisionEngine:
...
void addResponse(std::shared_ptr<CollisionResponse> response) {
_response.insert({std::make_pair(response->getTag1(), response->getTag2()), response});

}

std::unordered_map<std:air<int, int>, std::shared_ptr<CollisionResponse>> _response;



Last but not least is the Python code:

class TestCollision(example.CollisionResponse):

def onStart(self):
print('derived class')
...

cr = CollisionResponse()
cr.addResponse(TestCollision())


Now, in the CollisionEngine class, I have a method that calls the onStart method from the CollisionResponse objects stored in _response. However, no matter what happens, the base implementation always get called. In debug, I can see that the PyCollisionResponse:nStart is called, but then execution goes inside the CollisionResponse:nStart, and not in the Python TestCollision.onStart.

I'm really struggling figuring out what's wrong!

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