[C++-sig] problems downcasting from C++ base class intrusive pointers to Python derived instances.

[Lucio Moser]

> I don't know how this possible. It does not matter what smart pointer you use
> you cannot downcast to Python class. This is just impossible. You only
> can downcast to the class defined in C++.
>   
Well, the reality is, it works for shared_ptr. If you compile the code 
you'll see it. Whatever boost.python is doing, it knows to downcast the 
shared_ptr for a C++ class to a python derived class. There should be a 
solution for intrusive_ptr too.

> After reading your post few times, I think I understand your question
> and unfortunately I cannot help.
> I have 2 advices to you:
>
> Try to use class wrapper(
> http://boost.org/libs/python/doc/tutorial/doc/html/python/exposing.html#python.class_virtual_functions
> ). May be this will help.
>
> Try to introduce pure virtual function to your classes. May be
> compiler will find
> for you the places, you make class "slicing"(
> http://www.informit.com/articles/printerfriendly.asp?p=31529&rl=1 )
>
>   
Thank you for the links. I'll check them out in detail. Although they do 
not seem related to the problem I'm facing. I'm not trying to redefine 
the virtual methods of the C++ class on the python derived class. I'm 
just creating a very simple derived python class, and I'm not getting it 
back if I send it to the C++ functions.
This is my simple Python derived class. I'm not redefining any method on it.

class Derived2(Derived):
    pass