Tricky binding question

["Wesley Smith" <wesley.hoke@...>]

Hi Lua list,
I'm writing some Lua bindings for a C++ library and I'd like the
binding to follow as much as possible the way the library is coded
from C++.  I'm adding higer-level bindings as well, but the base,
low-level bindings I want to closely parallel what a C++ program would
look like.  Here's what I'm binding:

class Voronoi
{

    public:
        const Delaunay & dual()
        {
            return dt;
        }

//everything else left out for simplicity

    protected:
         Delaunay dt;
};

The way this is typically used goes as follows

Voronoi v;
v.dual().is_infinite(point);

I'd like to use it like this in Lua

v = Voronoi()
v:dual(): is_infinite(point)

There are a few issues to address here.  First, I'm returning a const
reference in C++ and I'd like to enforce that constness in the Lua
interface.  Second, I don't want to make a new userdata from the
dual() function because I have the Delaunay class already fully bound
and this reference to a Delaunay class isn't quite the same because of
its constness.  The ideal situation would be for the call to insert to
actually call a function in the Voronoi class.  In general, I bind C++
classes as userdata that are also C++ classes as so:

Voronoi_udata : public Voronoi;

What I envision is have a function in the Voronoi_udata class:

static int delaunay_ is_infinite(lua_State *L)
{
     //get voronoi instance from lua state
      Voronoi_udata *v = to_udata(L, 1);
      v->dual().is_infinite(...);
}


So my question is how do I bind the "dual" field in the Voronoi
userdata metatable to get this behavior?  One thing I've thought of
are to have dual() return a table with all the valid functions of the
Delaunay class.  Can anyone think of another potentially better
solution?

thanks,
wes