[C++-sig] Raw constructor (i.e. combination of make_constructor and raw_function)

[Hans Meine]

On Monday 22 August 2005 15:33, Hans Meine wrote:
> > > But this gives the vector as first element of the args tuple to
> > > createVector().
> >
> > What's wrong with that?
>
> I tried some more ways (e.g. returning None), and found out that it's
>
>  MyVector &result((python::extract<MyVector &>(args[0])()));
>
> which is not working.  Your question indicates that it should be possible
> to initialize the object given as first parameter.  If so, how should I do
> that? I need access to the contained C++ object, or do I have to export
> internal functions to python in order to set the state of the
> "self"-object?

Actually, I don't understand what kind of object I get in args[0].  Obviously, 
this corresponds to the "self"-argument of python __init__ functions.  
Naively, I would expect that it carries some kind of default-constructed C++ 
object (which I would like to prevent in the first place, but anyhow).

But I fail to either extract<>() something useful from it, or manipulate the 
object through a TypeWrapper - e.g. I exported the vector's resize() function 
to python and do

    python::object result(args[0]);
    result.attr("resize")(size);

However, I always get the same error messages - that I cannot do with a 
"PythonVector" what I am trying to do (extraction/call methods) because a 
"vigra::PythonVector<float>" is expected, which is exactly the class wrapped 
with class_ as "PythonVector":

| ArgumentError: Python argument types in
|     PythonVector.resize(PythonVector, int)
| did not match C++ signature:
|     resize(vigra::PythonVector<float> {lvalue}, unsigned)

Maybe the "self"-object passed to the constructor is incomplete in some way?

Ciao, /  /
     /--/
    /  / ANS