Gabriel Becedillas wrote:

Hi, I'd like to have my custom smart_ptr behave like boost::shared_ptr regarding from_python conversions. To_python converstions work fine, but the problem arises when I have an instance to a derived class via a smart_ptr to the base class MySmartPtr<Base> and this has to be passed to a function receiving MySmartPtr<Derived>. If I use boost::shared_ptr this works just fine. I think I'm doing something wrong in MySmartPtr_from_python. I'm pasting a simplified version of my code:

------ BEGIN C++ CODE ------

// Dummy smart pointer class. template <typename T> class MySmartPtr { public: MySmartPtr() : m_P(NULL) { }

MySmartPtr(T* a_P) : m_P(a_P) { }

T* m_P; };

namespace boost { namespace python {

template <typename T> T* get_pointer(MySmartPtr<T> const& a_P) { return a_P.m_P; }

template <typename T> struct pointee< MySmartPtr<T> > { typedef T type; };

} // namespace python } // namespace boost

template <class T> struct MySmartPtr_from_python { static void* convertible(PyObject* p) { if (p == Py_None) return p;

return boost::python::converter::get_lvalue_from_python(p, boost::python::converter::registered< MySmartPtr<T>

...

::converters); }

static void construct(PyObject* source, boost::python::converter::rvalue_from_python_stage1_data* data) { void* const storage = ((boost::python::converter::rvalue_from_python_storage<MySmartPtr<T>

...

*)data)->storage.bytes;

if (data->convertible == source) // This is because convertible returned p if p was Py_None. new (storage) MySmartPtr<T>(); else new (storage) MySmartPtr<T>( *((MySmartPtr<T>*)data->convertible) );

data->convertible = storage; } };

class Base { public: virtual ~Base() {} };

class Derived : public Base { };

boost::shared_ptr<Base> build_ok() { return boost::shared_ptr<Base>(new Derived()); }

MySmartPtr<Base> build_fail() { return MySmartPtr<Base>(new Derived()); }

void test_ok(boost::shared_ptr<Derived> a_Derived) {}

void test_fail(MySmartPtr<Derived> a_Derived) {}

template <typename T> void register_MySmartPtr_conversions() { boost::python::register_ptr_to_python< MySmartPtr<Base> >();

boost::python::converter::registry::insert( &MySmartPtr_from_python<T>::convertible, &MySmartPtr_from_python<T>::construct, boost::python::type_id< MySmartPtr<T> >() ); }

BOOST_PYTHON_MODULE(bptest) { boost::python::class_<Base, boost::noncopyable> class_Base("Base", boost::python::no_init); boost::python::register_ptr_to_python< boost::shared_ptr<Base> >(); register_MySmartPtr_conversions<Base>();

boost::python::class_<Derived, boost::noncopyable, boost::python::bases<Base> > class_Derived("Derived", boost::python::no_init); boost::python::register_ptr_to_python< boost::shared_ptr<Derived> >(); register_MySmartPtr_conversions<Derived>();

boost::python::def("build_ok", build_ok); boost::python::def("test_ok", test_ok);

boost::python::def("build_fail", build_fail); boost::python::def("test_fail", test_fail); }

------ END C++ CODE ------

This python code fails to work:

import bptest

bptest.test_ok(bptest.build_ok()) bptest.test_fail(bptest.build_fail())

And this is the error that I get:

Boost.Python.ArgumentError: Python argument types in bptest.test_fail(Derived) did not match C++ signature: test_fail(class MySmartPtr<class Derived>)

Thanks in advance.

This function should be like this: template <typename T> void register_MySmartPtr_conversions() { boost::python::register_ptr_to_python< MySmartPtr<T> >(); boost::python::converter::registry::insert( &MySmartPtr_from_python<T>::convertible, &MySmartPtr_from_python<T>::construct, boost::python::type_id< MySmartPtr<T> >() ); } But its still failing. -- Gabriel Becedillas Developer CORE SECURITY TECHNOLOGIES

Gabriel Becedillas wrote:

Hi, I'd like to have my custom smart_ptr behave like boost::shared_ptr regarding from_python conversions. To_python converstions work fine, but the problem arises when I have an instance to a derived class via a smart_ptr to the base class MySmartPtr<Base> and this has to be passed to a function receiving MySmartPtr<Derived>. If I use boost::shared_ptr this works just fine. I think I'm doing something wrong in MySmartPtr_from_python. I'm pasting a simplified version of my code:

------ BEGIN C++ CODE ------

// Dummy smart pointer class. template <typename T> class MySmartPtr { public: MySmartPtr() : m_P(NULL) { }

MySmartPtr(T* a_P) : m_P(a_P) { }

T* m_P; };

namespace boost { namespace python {

template <typename T> T* get_pointer(MySmartPtr<T> const& a_P) { return a_P.m_P; }

template <typename T> struct pointee< MySmartPtr<T> > { typedef T type; };

} // namespace python } // namespace boost

template <class T> struct MySmartPtr_from_python { static void* convertible(PyObject* p) { if (p == Py_None) return p;

return boost::python::converter::get_lvalue_from_python(p, boost::python::converter::registered< MySmartPtr<T>

...

::converters); }

static void construct(PyObject* source, boost::python::converter::rvalue_from_python_stage1_data* data) { void* const storage = ((boost::python::converter::rvalue_from_python_storage<MySmartPtr<T>

...

*)data)->storage.bytes;

if (data->convertible == source) // This is because convertible returned p if p was Py_None. new (storage) MySmartPtr<T>(); else new (storage) MySmartPtr<T>( *((MySmartPtr<T>*)data->convertible) );

data->convertible = storage; } };

class Base { public: virtual ~Base() {} };

class Derived : public Base { };

boost::shared_ptr<Base> build_ok() { return boost::shared_ptr<Base>(new Derived()); }

MySmartPtr<Base> build_fail() { return MySmartPtr<Base>(new Derived()); }

void test_ok(boost::shared_ptr<Derived> a_Derived) {}

void test_fail(MySmartPtr<Derived> a_Derived) {}

template <typename T> void register_MySmartPtr_conversions() { boost::python::register_ptr_to_python< MySmartPtr<Base> >();

boost::python::converter::registry::insert( &MySmartPtr_from_python<T>::convertible, &MySmartPtr_from_python<T>::construct, boost::python::type_id< MySmartPtr<T> >() ); }

BOOST_PYTHON_MODULE(bptest) { boost::python::class_<Base, boost::noncopyable> class_Base("Base", boost::python::no_init); boost::python::register_ptr_to_python< boost::shared_ptr<Base> >(); register_MySmartPtr_conversions<Base>();

boost::python::class_<Derived, boost::noncopyable, boost::python::bases<Base> > class_Derived("Derived", boost::python::no_init); boost::python::register_ptr_to_python< boost::shared_ptr<Derived> >(); register_MySmartPtr_conversions<Derived>();

boost::python::def("build_ok", build_ok); boost::python::def("test_ok", test_ok);

boost::python::def("build_fail", build_fail); boost::python::def("test_fail", test_fail); }

------ END C++ CODE ------

This python code fails to work:

import bptest

bptest.test_ok(bptest.build_ok()) bptest.test_fail(bptest.build_fail())

And this is the error that I get:

Boost.Python.ArgumentError: Python argument types in bptest.test_fail(Derived) did not match C++ signature: test_fail(class MySmartPtr<class Derived>)

Thanks in advance.

I also forgot to say that upcasts aren't working either. If I return a MySmartPtr<Base> and the concrete type is Derived, boost::python let me use the Derived interface (which is great!), but when this instance has to be passed back to C++ it'll only match an exact MySmartPtr<T> type. It won't do neither an upcast nor a downcast. After checking shared_ptr_from_python a litte bit I realize that convertible(...) is returning a raw T* to the object (when the passed PyObject is not Py_None) and that construct(...) is creating a new boost::shared_ptr from the raw T*. converter::get_lvalue_from_python(p, registered<T>::converters) is used to extract the raw T* from the PyObject. This won't work for me because I need to extract the whole MySmartPtr<T>*, not just the raw T*, in order to copy the MySmartPtr<T> in construct(...). Is there a way to do that ? Please keep in mind that I need to check both for upcasts and downcasts. My PyObject could hold a MySmartPtr<Derived> instance and I'd like to pass it to C++ as a MySmartPtr<Base>, and the other way around (previously checking if a downcast is possible). I really need to make MySmartPtr<T> to behave as boost::shared_ptr<T> regarding conversions. Thanks a lot.