[C++-sig] Member overloads signature not matching C++ signature

July 30, 2015

      I am trying to bind a C++ class but python is reporting there is no 
matching signature for two of the methods which are I am trying to bind 
using the member function overloads macro.

The class looks like so:

     struct path {
         path();
         path(double line_width);

         void move_to(point_t point);
         void line_to(point_t point);
         void curve_to(std::array<point_t, 3>&& points)
         void curve_to(const std::array<point_t, 3>& points);
         void fill(context& ctx, bool close = true) const;
         void stroke(context& ctx, bool close = true) const;
     };

I'm not sure if this is the best way but I have made a thin wrapper 
around the class such that the curve_to method can be called with a tuple:

     struct path_wrapper : path {
         using path::path;

         void curve_to(const py::tuple& points)
         {
             path::curve_to({
                 py::extract<path::point_t>(points[0]),
                 py::extract<path::point_t>(points[1]),
                 py::extract<path::point_t>(points[2]),
             });
         }
     };

The function overloads are being defined as such:

     BOOST_PYTHON_MEMBER_FUNCTION_OVERLOADS(
         path_fill_overloads, fill, 1, 2
     );

     BOOST_PYTHON_MEMBER_FUNCTION_OVERLOADS(
         path_stroke_overloads, stroke, 1, 2
     );

I then bind the class as such:

     py::class_<path_wrapper>("Path")
         .def(py::init<double>())
         .def("move_to", &path::move_to)
         .def("line_to", &path::line_to)
         .def("curve_to", &path_wrapper::curve_to)
         .def("fill", &path::fill, path_fill_overloads())
         .def("stroke", &path::stroke,  path_stroke_overloads());

I am binding the other classes named throughout this process, but I have 
omitted their actual class_ calls from this message.

When I make a call to the methods in python I recieve the following error:

     Traceback (most recent call last):
       File "/home/james/projects/imgen/patterns/triangles.py", line 46, 
in draw
         path.stroke(context)
     Boost.Python.ArgumentError: Python argument types in
         Path.stroke(Path, Context)
     did not match C++ signature:
         stroke(path {lvalue}, context {lvalue})
         stroke(path {lvalue}, context {lvalue}, bool)

I am really confused as the signatures appear to match. I suspect I've 
broken the converters with my wrapper class but I am unsure how to fix it.

Thank you.

[C++-sig] Member overloads signature not matching C++ signature

James Maddison