[C++-sig] Problems with custom smart pointers and multiple inheritance

[Alex Mohr]

>      print c1.PassAPointer(c1)   # fails
> Boost.Python.ArgumentError: Python argument types in 
> MyBaseA.PassAPointer(MyClass, MyClass) did not match C++ signature:
>      PassAPointer(class MyNamespace::MyBaseA {lvalue}, class 
> MyNamespace::MyPointer<class MyNamespace::MyBaseA>)

Have you tried using MyPointer<T> as the held types?  That is:

class_<MyBaseA, MyPointer<MyBaseA>, boost::noncopyable>
class_<MyBaseB, MyPointer<MyBaseB>, boost::noncopyable>
class_<MyClass, MyPointer<MyClass>, boost::noncopyable, bases<...> >

Then you shouldn't need register_ptr_to_python (only when you get to 
polymorphism and the classes you are wrapping are really wrapper<T>).

> * I need to know the PyObject wrapping my C++ class instance, but the 
> "class syntax #2" invoking the constructor taking a PyObject as 
> parameter works even worse.

If you read the docs for class_ where it talks about HeldType semantics, 
you'll see info regarding 'has_back_reference'.  That may work for you.

> * The Python object returned by 'GetBaseA()' is not the same as the 
> calling Python object although they are actually referencing the same 
> C++ class instance. Is there any way to avoid this ? (this is not the 
> biggest of my problems though)

If you use boost::shared_ptr, it sort of works.  With any other smart 
pointer you can't really do it as far as I know.  There's some ongoing 
discussion about this.  I would like to fix it.

By the way, injecting constructors via make_constructor is not going to 
work for you if/when you try to expose these classes as polymorphic to 
python.  This is because make_constructor doesn't seem to cause 
boost::python::detail::initialize_wrapper() to be called.  Seems like it 
maybe could/should.  I've cobbled together my own make_constructor in 
order to work around this, so if you run into that, perhaps I can help.

Alex