shared_ptr for stl types. Getting "Holder classes are only supported for custom types"

[DmitriGoloubentsev]

Hi all,

I'm trying to support C++ interfaces there shared_ptr<> is used to hold stl types such as std::vector<> etc. I'm getting "Holder classes are only supported for custom types" and saw suggestions to make enclosing type as OPAQUE. But this means more trouble on python side and custom classes.

I don't mind if data is copied and happy to use default stl binder. How do I achieve this for processVector and processVectorofA?

processVectorofA2 - works fine now, and I don't understand why processVector and processVectorofA fail.

Kind regards,
Dmitri.

`
#include <pybind11/pybind11.h>
#include <pybind11/stl.h>
// #include <pybind11/stl_bind.h>
#include
#include
#include

namespace py = pybind11;

void processVector(const std::shared_ptr<std::vector>& vec) {
// Example processing
for (double val : *vec) {
std::cout << val << std::endl;
}
}
class A {
public:
A() = default;
A(int i) : i(i) {}
int i;
};

void processVectorofA(const std::shared_ptr<std::vector>& vec) {
// Example processing
for (const A& val : *vec) {
std::cout << val.i << std::endl;
}
}

void processVectorofA2(const std::vector& vec) {
// Example processing
for (const A& val : vec) {
std::cout << val.i << std::endl;
}
}

PYBIND11_MODULE(example, m) {
py::class_(m, "A")
.def(py::init())
.def_readwrite("i", &A::i);

m.def("process_vector", &processVector, "A function that processes a vector of doubles",
      py::arg("vec"));

m.def("process_vector_of_A", &processVectorofA, "A function that processes a vector of A",
        py::arg("vec"));

m.def("process_vector_of_A2", &processVectorofA2, "A function that processes a vector of A",
        py::arg("vec"));

}
`

Compilation command:
clang++ -I./pybind11/include/ -c test_pybind.cpp -isystem /usr/include/python3.11

Error message:
`
In file included from test_pybind.cpp:1:
In file included from ./pybind11/include/pybind11/pybind11.h:13:
In file included from ./pybind11/include/pybind11/detail/class.h:12:
In file included from ./pybind11/include/pybind11/attr.h:14:
./pybind11/include/pybind11/cast.h:746:5: error: static_assert failed due to requirement 'std::is_base_of<pybind11::detail::type_caster_base<std::vector<double, std::allocator>>, pybind11::detail::type_caster<std::vector<double, std::allocator>, void>>::value' "Holder classes are only supported for custom types"
static_assert(std::is_base_of<base, type_caster>::value,
^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
./pybind11/include/pybind11/cast.h:820:48: note: in instantiation of template class 'pybind11::detail::copyable_holder_caster<std::vector, std::shared_ptr<std::vector>>' requested here
class type_caster<std::shared_ptr> : public copyable_holder_caster<T, std::shared_ptr> {};
^
./pybind11/include/pybind11/cast.h:1404:57: note: in instantiation of template class 'pybind11::detail::type_caster<std::shared_ptr<std::vector>>' requested here
static constexpr auto arg_names = concat(type_descr(make_caster::name)...);
^
./pybind11/include/pybind11/pybind11.h:219:34: note: in instantiation of template class 'pybind11::detail::argument_loader<const std::shared_ptr<std::vector> &>' requested here
sizeof...(Args), cast_in::args_pos >= 0, cast_in::has_kwargs),
^
./pybind11/include/pybind11/pybind11.h:92:9: note: in instantiation of function template specialization 'pybind11::cpp_function::initialize<void (&)(const std::shared_ptr<std::vector> &), void, const std::shared_ptr<std::vector> &, pybind11::name, pybind11::scope, pybind11::sibling, char[46], pybind11::arg>' requested here
initialize(f, f, extra...);
^
./pybind11/include/pybind11/pybind11.h:1163:22: note: in instantiation of function template specialization 'pybind11::cpp_function::cpp_function<void, const std::shared_ptr<std::vector> &, pybind11::name, pybind11::scope, pybind11::sibling, char[46], pybind11::arg>' requested here
cpp_function func(std::forward(f),
^
test_pybind.cpp:42:7: note: in instantiation of function template specialization 'pybind11::module_::def<void ()(const std::shared_ptr<std::vector> &), char[46], pybind11::arg>' requested here
m.def("process_vector", &processVector, "A function that processes a vector of doubles",
^
In file included from test_pybind.cpp:1:
./pybind11/include/pybind11/pybind11.h:219:41: error: incomplete definition of type 'pybind11::detail::argument_loader<const std::shared_ptr<std::vector> &>'
sizeof...(Args), cast_in::args_pos >= 0, cast_in::has_kwargs),
~~~~~~~^~
./pybind11/include/pybind11/pybind11.h:92:9: note: in instantiation of function template specialization 'pybind11::cpp_function::initialize<void (&)(const std::shared_ptr<std::vector> &), void, const std::shared_ptr<std::vector> &, pybind11::name, pybind11::scope, pybind11::sibling, char[46], pybind11::arg>' requested here
initialize(f, f, extra...);
^
./pybind11/include/pybind11/pybind11.h:1163:22: note: in instantiation of function template specialization 'pybind11::cpp_function::cpp_function<void, const std::shared_ptr<std::vector> &, pybind11::name, pybind11::scope, pybind11::sibling, char[46], pybind11::arg>' requested here
cpp_function func(std::forward(f),
^
test_pybind.cpp:42:7: note: in instantiation of function template specialization 'pybind11::module_::def<void ()(const std::shared_ptr<std::vector> &), char[46], pybind11::arg>' requested here
m.def("process_vector", &processVector, "A function that processes a vector of doubles",
^
In file included from test_pybind.cpp:1:
In file included from ./pybind11/include/pybind11/pybind11.h:13:
In file included from ./pybind11/include/pybind11/detail/class.h:12:
In file included from ./pybind11/include/pybind11/attr.h:14:
./pybind11/include/pybind11/cast.h:746:5: error: static_assert failed due to requirement 'std::is_base_of<pybind11::detail::type_caster_base<std::vector<A, std::allocator>>, pybind11::detail::type_caster<std::vector<A, std::allocator>, void>>::value' "Holder classes are only supported for custom types"
static_assert(std::is_base_of<base, type_caster>::value,
^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
./pybind11/include/pybind11/cast.h:820:48: note: in instantiation of template class 'pybind11::detail::copyable_holder_caster<std::vector, std::shared_ptr<std::vector>>' requested here
class type_caster<std::shared_ptr> : public copyable_holder_caster<T, std::shared_ptr> {};
^
./pybind11/include/pybind11/cast.h:1404:57: note: in instantiation of template class 'pybind11::detail::type_caster<std::shared_ptr<std::vector>>' requested here
static constexpr auto arg_names = concat(type_descr(make_caster::name)...);
^
./pybind11/include/pybind11/pybind11.h:219:34: note: in instantiation of template class 'pybind11::detail::argument_loader<const std::shared_ptr<std::vector> &>' requested here
sizeof...(Args), cast_in::args_pos >= 0, cast_in::has_kwargs),
^
./pybind11/include/pybind11/pybind11.h:92:9: note: in instantiation of function template specialization 'pybind11::cpp_function::initialize<void (&)(const std::shared_ptr<std::vector> &), void, const std::shared_ptr<std::vector> &, pybind11::name, pybind11::scope, pybind11::sibling, char[40], pybind11::arg>' requested here
initialize(f, f, extra...);
^
./pybind11/include/pybind11/pybind11.h:1163:22: note: in instantiation of function template specialization 'pybind11::cpp_function::cpp_function<void, const std::shared_ptr<std::vector> &, pybind11::name, pybind11::scope, pybind11::sibling, char[40], pybind11::arg>' requested here
cpp_function func(std::forward(f),
^
test_pybind.cpp:45:7: note: in instantiation of function template specialization 'pybind11::module_::def<void ()(const std::shared_ptr<std::vector> &), char[40], pybind11::arg>' requested here
m.def("process_vector_of_A", &processVectorofA, "A function that processes a vector of A",
^
In file included from test_pybind.cpp:1:
./pybind11/include/pybind11/pybind11.h:219:41: error: incomplete definition of type 'pybind11::detail::argument_loader<const std::shared_ptr<std::vector> &>'
sizeof...(Args), cast_in::args_pos >= 0, cast_in::has_kwargs),
~~~~~~~^~
./pybind11/include/pybind11/pybind11.h:92:9: note: in instantiation of function template specialization 'pybind11::cpp_function::initialize<void (&)(const std::shared_ptr<std::vector> &), void, const std::shared_ptr<std::vector> &, pybind11::name, pybind11::scope, pybind11::sibling, char[40], pybind11::arg>' requested here
initialize(f, f, extra...);
^
./pybind11/include/pybind11/pybind11.h:1163:22: note: in instantiation of function template specialization 'pybind11::cpp_function::cpp_function<void, const std::shared_ptr<std::vector> &, pybind11::name, pybind11::scope, pybind11::sibling, char[40], pybind11::arg>' requested here
cpp_function func(std::forward(f),
^
test_pybind.cpp:45:7: note: in instantiation of function template specialization 'pybind11::module_::def<void ()(const std::shared_ptr<std::vector> &), char[40], pybind11::arg>' requested here
m.def("process_vector_of_A", &processVectorofA, "A function that processes a vector of A",
^
4 errors generated.

`

[DmitriGoloubentsev]

Sorry, file got corrupted.

Here is the proper version.
test_pybind.zip