[C++-sig] Passing inherited classes back to C++

[Roman Yakovenko]

On 5/5/07, Tom Brooks <tgbrooks at gmail.com> wrote:
> I currently have these C++ classes:
>
> class Renderable
> {
> public:
>     Renderable();
>     virtual ~Renderable();
>     virtual void Draw() = 0;
> };
>
> class Quad : public Renderable
> {
> public:
>      Quad(float x, float y, float h, float w);
>     ~Quad();
>     void Draw();
> };
>
> And I need to expose them to Python. Then, I need to be able to make one in
> Python, and pass it back to a C++ function  as a Renderable*.
>
> I made this wrapper class for Renderable:
>
> struct RenderableWrap : Renderable, wrapper<Renderable>
> {
> public:
>     void Draw()
>     {
>         this->get_override("Draw")();
>     }
> };
>
> And I have this Boost.Python code for the Python side:
>
>     class_<RenderableWrap,
> boost::noncopyable>("Renderable")
>         .def("Draw",pure_virtual(&Renderable::Draw))
>     ;
>
>     class_<Quad, bases<RenderableWrap> >("Quad",init<float, float, float,

Quad derives from Renderable, not RenderableWrap

> float>())
>         .def("Draw",&Quad::Draw)
>     ;
>
> But when I pass in a Quad() to my C++ function, I get an error that it can't
> convert from a Quad to a Renderable*. I have next to no clue how the base
> class should have been done, since the tutorial and anything else I can find
> online don't go over what to do for the base class (when there are virtual
> functions, at least). For example, I don't know if I inherit from
> Renderable, or RenderableWrap (or both?). I don't know whether the base
> class needs a wrapper itself (and would it if it had a virtual function?).
>
> I'd appreciate any help!

Next code was generated by Py++ GUI
(http://language-binding.net/pyplusplus/documentation/tutorials/pyplusplus_gui.html)

#include "boost/python.hpp"

#include "1.h"

namespace bp = boost::python;

struct Renderable_wrapper : Renderable, bp::wrapper< Renderable > {

    Renderable_wrapper( )
    : Renderable( )
      , bp::wrapper< Renderable >(){
        // null constructor

    }

    virtual void Draw(  ){
        bp::override func_Draw = this->get_override( "Draw" );
        func_Draw(  );
    }

};

struct Quad_wrapper : Quad, bp::wrapper< Quad > {

    Quad_wrapper(Quad const & arg )
    : Quad( arg )
      , bp::wrapper< Quad >(){
        // copy constructor

    }

    Quad_wrapper(float x, float y, float h, float w )
    : Quad( x, y, h, w )
      , bp::wrapper< Quad >(){
        // constructor

    }

    virtual void Draw(  ) {
        if( bp::override func_Draw = this->get_override( "Draw" ) )
            func_Draw(  );
        else
            this->Quad::Draw(  );
    }


    void default_Draw(  ) {
        Quad::Draw( );
    }

};

BOOST_PYTHON_MODULE(pyplusplus){
    bp::class_< Renderable_wrapper, boost::noncopyable >( "Renderable" )
        .def( bp::init< >() )
        .def(
            "Draw"
            , bp::pure_virtual( &::Renderable::Draw ) );

    bp::class_< Quad_wrapper, bp::bases< Renderable > >( "Quad",
bp::init< float, float, float, float >(( bp::arg("x"), bp::arg("y"),
bp::arg("h"), bp::arg("w") )) )
        .def(
            "Draw"
            , &::Quad::Draw
            , &Quad_wrapper::default_Draw );
}


-- 
Roman Yakovenko
C++ Python language binding
http://www.language-binding.net/