If I try to return a unique pointer to a pure virtual class it fails due to
return_value_policy = move, but the object is neither movable nor copyable!
However it if the class is not pure virtual it works fine. Same for returning a shared pointer to it.
Below is a minimal working example based on the docs
#include <pybind11/pybind11.h>
namespace py = pybind11;
class Animal {
public:
virtual ~Animal() { }
virtual std::string go(int n_times) = 0;
};
class Dog : public Animal {
public:
std::string go(int n_times) override {
std::string result;
for (int i=0; i<n_times; ++i)
result += "woof! ";
return result;
}
};
class PyAnimal : public Animal {
public:
/* Inherit the constructors */
using Animal::Animal;
/* Trampoline (need one for each virtual function) */
std::string go(int n_times) override {
PYBIND11_OVERLOAD_PURE(
std::string, /* Return type */
Animal, /* Parent class */
go, /* Name of function in C++ (must match Python name) */
n_times /* Argument(s) */
);
}
};
std::unique_ptr<Animal> build_dog() {
return std::unique_ptr<Animal>(new Dog{});
}
std::shared_ptr<Animal> build_shared_dog() {
return std::shared_ptr<Animal>(new Dog{});
}
PYBIND11_PLUGIN(PyAUSA) {
py::module m("PyAUSA", "Python bindings for AUSAlib");
py::class_<Animal, PyAnimal /* <--- trampoline*/> animal(m, "Animal");
animal
.def(py::init<>())
.def("go", &Animal::go);
py::class_<Dog>(m, "Dog", animal)
.def(py::init<>());
m.def("build_dog", &build_dog);
m.def("build_shared_dog", &build_shared_dog);
return m.ptr();
}Output:
In [1]: import PyAUSA
In [2]: PyAUSA.build_shared_dog()
Out[2]: <PyAUSA.Dog at 0x7fab45d1d7e0>
In [3]: PyAUSA.build_dog()
---------------------------------------------------------------------------
RuntimeError Traceback (most recent call last)
<ipython-input-3-d86cdac6dbbe> in <module>()
----> 1 PyAUSA.build_dog()
RuntimeError: return_value_policy = move, but the object is neither movable nor copyable!
If I try to return a unique pointer to a pure virtual class it fails due to
However it if the class is not pure virtual it works fine. Same for returning a shared pointer to it.
Below is a minimal working example based on the docs
Output: