[Python] Bug when exporting function overloaded on base and derived classes

9 Feb 2007

      Hi,
 I've found a bug where Boost.Python calls the wrong function overload. Here
is a small unit test:

=====
The C++ module "_test.cpp":
=====

#include <boost/python.hpp>
#include <string>

class Base { };

class Derived : public Base { };

std::string f(Base& b) {
    return "Base";
}

std::string f(Derived& d) {
    return "Derived";
}

BOOST_PYTHON_MODULE( _test )
{
    using namespace boost::python;

    class_<Base>("Base");
    class_<Derived, bases<Base> >("Derived");

    def("f", static_cast<std::string (*)(Derived&)>(&f));
    def("f", static_cast<std::string (*)(Base&)>(&f));
}

=====
The small test in python:
=====
...
...
...
from _test import *
f(Base())
'Base'
f(Derived())
'Base'
=====

Interestingly enough, if the function overloads are exported in the inverse
order, it actually works, i.e., if using this code:

=====
BOOST_PYTHON_MODULE( _test )
{
    using namespace boost::python;

    class_<Base>("Base");
    class_<Derived, bases<Base> >("Derived");

    def("f", static_cast<std::string (*)(Base&)>(&f));
    def("f", static_cast<std::string (*)(Derived&)>(&f));
}
=====

I do not know very well how does the boost.python registry works, but it
seems that it is selecting the first match instead of testing all matches
and selecting the "best one".

Edson Tadeu

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