The first thing we'll do is create a Tag for the VTK framework, in namespace boost::dataflow::vtk. All we have to do is inherit from default_tag:

namespace boost { namespace dataflow { namespace vtk {

// The vtk framework tag
struct tag : public default_tag {};

} } } // namespace boost::dataflow::vtk

We can now use it to tag all of our VTK support classes.

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Setting up a producer Port and a consumer Port