I've got a very large and mature C++ code base that I'm trying to use SWIG on to generate a C# interface for. I cannot change the actual C++ code itself but we can use whatever SWIG offers in the way of extending/updating it. I'm facing an issue where a function C++ is written as such:

A* SomeClass::next(A*)

The caller might do something like:

A* acurr = 0;
while( (acurr = sc->next(acurr)) != 0 ){
    if( acurr isoftype B ){
        B* b = (B*)a;
        ...do some stuff with b..
    }
    elseif( acurr isoftype C )
    ...
}

Essentially, iterating through a container elements that depending on their true type, do something different. The SWIG generated C# layer for the "next" function unfortunately does the following:

return new A();

So the calling code in C# land cannot determine if the returned object is actually a derived class or not, it actually appears to always be the base class (which does make sense). I've come across several solutions:

1. Use the %extend SWIG keyword to add a method on an object and ultimately call dynamic_cast. The downside to this approach, as I see it, is that this requires you to know the inheritance hierarchy. In my case it is rather huge and I see this is as a maintenance issue.
2. Use the %factory keyword to supply the method and the derived types and have SWIG automatically generate the dynamic_cast code. This appears to be a better solution that the first, however upon a deeper look it still requires you to hunt down all the methods and all the possible derived types it could return. Again, a huge maintenance issue. I wish I had a doc link for this but I can't find one. I found out about this functionality by looking through the example code that comes with SWIG.

3. Create a C# method to create an instance of the derived object and transfer the cPtr to the new instance. While I consider this clumsy, it does work. See an example below.

   public static object castTo(object fromObj, Type toType) { object retval = null;

   BaseClass fromObj2 = fromObj as BaseClass;
   HandleRef hr = BaseClass.getCPtr(fromObj2);
   IntPtr cPtr = hr.Handle;
   object toObj = Activator.CreateInstance(toType, cPtr, false);
   
   
   // make sure it actually is what we think it is
   if (fromObj.GetType().IsInstanceOfType(toObj))
   {
       return toObj;
   }
   
   
   return retval;
   

   }

Are these really the options? And if I'm not willing to dig through all the existing functions and class derivations, then I'm left with #3? Any help would be appreciated.