I am trying to get raw pointers and abstract base classes working
properly with boost::python v2. I am working on an example inspired
by the tutorial
http://www.boost.org/libs/python/doc/tutorial/doc/inheritance.html.
In my case, the base class has a pure virtual function, but I don't
need to override it in python and call it from c++, so I don't think I
need to do a BaseWrap.
The problem is that if I try and expose Base to python, I get the
compiler (gcc 3.2) error:
g++ -isystem/usr/local/include -I/usr/local/include/python2.2 -fPIC -ftemplate-depth-100 -c rawpointer.cpp
/usr/local/include/boost/python/object/value_holder.hpp: In instantiation of `boost::python::objects::value_holder<Base>':
/usr/local/include/boost/type_traits/alignment_of.hpp:52: instantiated from `boost::detail::alignment_of_impl'
/usr/local/include/boost/python/object/instance.hpp:29: instantiated from `boost::alignment_of'
...snip...
rawpointer.cpp:47: instantiated from here
/usr/local/include/boost/python/object/value_holder.hpp:36: cannot declare
field `boost::python::objects::value_holder<Base>::m_held' to be of type `
Base'
/usr/local/include/boost/python/object/value_holder.hpp:36: because the
following virtual functions are abstract:
rawpointer.cpp:15: virtual const std::string& Base::get_name()
rawpointer.cpp:14: virtual void Base::sayit() const
make: *** [rawpointer.o] Error 1
and if I only expose the derived classes, the code compiles but then I
get a runtime error when I try and import the class in python
import rawpointer
Traceback (most recent call last):
File "<stdin>", line 1, in ?
RuntimeError: extension class wrapper for base class 4Base has not been created
yet
Below is my example code. Suggestions welcomed!
John Hunter
// work with raw pointers
#include <iostream>
#include <string>
#include
#include
using namespace boost::python;
class Base {
public:
virtual ~Base() {};
virtual void sayit() const=0;
virtual const std::string& get_name()=0;
private:
};
class Foo : public Base {
public:
Foo() : _name("Foo") {}
void sayit() const { std::cout << "Foo" << std::endl; }
const std::string& get_name() {return _name;}
private:
const std::string _name;
};
class Bar : public Base {
public:
Bar() : _name("Bar") {}
void sayit() const { std::cout << "Bar" << std::endl; }
const std::string& get_name() {return _name;}
private:
const std::string _name;
};
Base* barfactory(){ return new Bar(); }
Base* foofactory(){ return new Foo(); }
std::string simonsays(Base* p) {return p->get_name();}
BOOST_PYTHON_MODULE_INIT(rawpointer)
{
class_<Base>("Base", no_init)
.def("sayit", &Base::sayit);
class_("Foo")
.def("sayit", &Foo::sayit);
class_("Bar")
.def("sayit", &Bar::sayit);
def("foofactory", foofactory, return_value_policy());
def("barfactory", barfactory, return_value_policy());
def("simonsays", simonsays);
}
