[C++-sig] Overloading methods in derived class

[Jeremy Mayes]

Hi,

I’m wrapping a 3rd party library using boost.python and I’m bumping into a
frustrating pattern. The library has derived classes which overload methods
in their base class. They do properly expose the base class’ methods using
“using”, but, when I try to wrap all of these derived classes, python
doesn’t see the base class’ method through an instance of the derived
class. Here’s an example:

#include <boost/python.hpp>

using namespace boost::python;

struct A {
    virtual void foo(int a) {}
    virtual void bar(double b) {}
};

struct B : A {
    virtual void foo(int a, double b) {}
};

BOOST_PYTHON_MODULE(broken)
{
    class_<A>(“A”)
        .def(“foo”, &A::foo)
        .def(“bar”, &A::bar)
    ;

    class_<B, bases<A> >(“B”)
        .def(“foo”, &B::foo)
    ;
}


Then in python:

import broken

a = broken.A()
b = broken.B()

a.foo(1)
a.bar(2.0)

b.foo(1,2.0)
b.bar(2.0)
b.foo(0)


Running this I get (as you’ve probably already guessed):

File “.../test.py”, line 11, in <module>
    b.foo(0)
Boost.Python.ArgumentError: Python argument types in
    B.foo(B, int)
Did not match C++ signature:
    foo(B {Value}, int, double)

I’m not surprised by this behavior given python’s method resolution
process. My question is whether there’s a good way to deal with this in
boost.python so that I don’t have to add duplicate entries in sub-classes
for methods I’ve already exposed in base classes.

Thanks,
Jeremy
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