[Boost-users] [Python] Wrapping Visitor Pattern and Object Slicing

Subject: [Boost-users] [Python] Wrapping Visitor Pattern and Object Slicing
From: Alex Olivas (olivas_at_[hidden])
Date: 2011-12-27 16:21:51

Hey All,
I'm trying to wrap a third party lib that uses the visitor
pattern and their own smart pointers ('ref_ptr' below), which
manages objects that inherit from 'Referenced'.  I've put
together a simple example that illustrates the problem.

Code for python bindings : http://codepad.org/wq47m5CI
Simple test script : http://codepad.org/Jfme3U6U
Output for two cases : http://codepad.org/gbFBxy04
    Case 1) 'apply' override is commented out in the python class
    Case 2) 'apply' override exists

The problem that I'm having is that the 'apply' method
( lines 83 - 86 ) slices everything to base unless I use
boost::ref().  However this only works for wrapped classes
and in this lib several classes use derived visitors that
are not part of the public API ( which I modeled as HelperVisitor
in the above example ).

Is there anyway to prevent object slicing for both wrapped
and unwrapped objects in this scenario?

I'm building against boost 1.47 and if anyone's interested in
digging deeper the 3rd party lib is Open Scene Graph 3.0.1.

Thanks,
Alex.