[C++-sig] How to expose virtual function with default arguments in boost.python ?

[Baptiste Lepilleur]

I'm trying to fix a bug in Pyste regarding exposure of virtual function with
default arguments, but I can't figure out what is the correct code to
generate (e.g. this is a question regarding boost.python, not pyste).

I'm basically trying to expose the virtual member function 'set' of the
following code:

----
class VirtualNonCopyable {
public:
   virtual void set( const std::string &name_, int size_ = 10, int width_ =
12 ) {
      name = name_;
      size = size_;
      width = width_;
   }

   std::string name;
   int size;
   int width;
};

inline VirtualNonCopyable &getVirtualNonCopyable() {
   static VirtualNonCopyable instance;
   return instance;
}
----

Pyste generate the following binding code (full source attached):

----
    class_< VirtualNonCopyable, py::VirtualNonCopyable_Wrapper
>("VirtualNonCopyable", init<  >())
        .def("set", &VirtualNonCopyable::set,
&py::VirtualNonCopyable_Wrapper::default_set_3)
        .def("set", &py::VirtualNonCopyable_Wrapper::default_set_1)
        .def("set", &py::VirtualNonCopyable_Wrapper::default_set_2)
        .def(init< const VirtualNonCopyable& >())
        .def_readwrite("name", &VirtualNonCopyable::name)
        .def_readwrite("size", &VirtualNonCopyable::size)
        .def_readwrite("width", &VirtualNonCopyable::width)
    ;
----
Pyste is still using old-style polymorphism. default_set_1, default_set_2
and default_set_3 are methods forwarding to the base class implementation.
The binding for default_set_1 should be the one triggered by the python code
below.

The bug is demonstrated by the following python code:

object = getVirtualNonCopyable()   # Get a instance of VirtualNonCopyable
from C++
object.set( 'abc' )                             # use overloading resolution
to apply the default values

Which produces the following error:

    object.set( 'abc' )
Boost.Python.ArgumentError: Python argument types in
    VirtualNonCopyable.set(VirtualNonCopyable, str)
did not match C++ signature:
    set(struct py::VirtualNonCopyable_Wrapper {lvalue}, class
std::basic_string<char,struct std::char_traits<char>,class
std::allocator<char> >, int)
    set(struct py::VirtualNonCopyable_Wrapper {lvalue}, class
std::basic_string<char,struct std::char_traits<char>,class
 std::allocator<char> >)
    set(struct py::VirtualNonCopyable_Wrapper {lvalue}, class
std::basic_string<char,struct std::char_traits<char>,class
 std::allocator<char> >, int, int)
    set(class VirtualNonCopyable {lvalue}, class
std::basic_string<char,struct std::char_traits<char>,class std::allocat
or<char> >, int, int)

The issue only occurs when the object is returned from C++ and all the
parameters are not specified. The following python code works correctly:
object = getVirtualNonCopyable()
object.set( 'abc', 1, 2 )                        # works with all parameters
specified

object = VirtualNonCopyable()
object.set( 'abc' )                                # works on instance
created in python

I couldn't find any example of combining default argument handling with
default virtual method implementation. Does anyone know how to do so ?

Baptiste.
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