[C++-sig] Custom smart pointer progress (I think?)

[Alex Mohr]

I have come up with what seems to be an initial solution to the problems 
I posted yesterday regarding smart pointers that are not shared_ptr.

Digging into boost python, I found converter/shared_ptr_from_python.hpp. 
  I followed its lead and did something like the code below.

If I instantiate one of these SmartPtrFromPython<T> for each T that has 
SmartPtr as the held type, then the broken examples I posted yesterday 
seem to work as I would expect, just like in the shared_ptr case.

Of course this seems a bit questionable.  I think I'm dealing with 
private API, and I don't really know if registering these converters is 
potentially dangerous.  Is this a reasonable approach?

Thanks,

Alex


using namespace boost::python;

template <typename T>
struct SmartPtrFromPython {
     SmartPtrFromPython() {
         converter::registry::insert(&convertible, &construct,
             type_id<SmartPtr<T> >());
     }
   private:
     static void *convertible(PyObject *p) {
         if (p == Py_None)
             return p;
         return converter::get_lvalue_from_python(p,
             converter::registered<T>::converters);
     }
     static void construct(PyObject *source, converter::
         rvalue_from_python_stage1_data *data) {
         void *const storage = ((converter::
             rvalue_from_python_storage<SmartPtr<T> >*)data)->
             storage.bytes;
         // None case:
         if (data->convertible == source)
             new (storage) SmartPtr<T>();
         else
             new (storage) SmartPtr<T>
                 (static_cast<T*>(data->convertible));
         data->convertible = storage;
     }
}