Downcast issue with ColaTopologyAddon when using the C# bindings

[foolnotion]

Hello,

I am using the four adaptagrams libraries on windows, via the C# bindings generated with SWIG. Basic layouting and edge routing works, however I am trying to use the topology preserving addon using the Dunnart code as an example (is there any other documentation available?). It goes like this:

layout = new ConstrainedFDLayout(rectangles, edges, idealEdgeLength, true);
// passing libcola an empty instance of this class will cause it to populate it 
// with the current topology information for nodes and edges when layout.makeFeasible() is run
var topology = new ColaTopologyAddon();
layout.setTopology(topology);
layout.makeFeasible();
layout.run();

var nodes = topology.topologyNodes; //  nodes count is zero
var routes = topology.topologyRoutes; // routes count is zero

var newTopology = (ColaTopologyAddon)layout.getTopology(); // cast exception

The issue is that the getTopology() method returns an instance of the base class TopologyAddonInterface which cannot be downcasted in C#. This sounds like a problem with the SWIG-generated bindings (after I've read some related issues here http://johnnado.com/swig-csharp-java-downcast/).

Any ideas? Thanks.

[foolnotion]

This issue can be resolved by adapting the swig interface:

%extend topology::ColaTopologyAddon {
    static topology::ColaTopologyAddon * CastToConcreteType(cola::TopologyAddonInterface *obj) {
        return dynamic_cast<topology::ColaTopologyAddon*>(obj);
    }
}

The above code inserts a static method in the ColaTopologyAddon generated class which makes use of the underlying dynamic_cast to produce the correct result. This can then be used like this:

var topologyInterface = layout.getTopology();
topology = ColaTopologyAddon.CastToConcreteType(topologyInterface);