[vtk-developers] protected private storage class pointers?

[Eric E. Monson]

Hey Marcus,

I'm revisiting my subclasses of some of the Charts stuff to see whether I can make it easier to maintain as you guys improve VTK. (I add some members to keep track of another set of selections and I need to customize the Paint() routines to display different annotations and decorations.)

In some cases (especially with parallel coordinates plot and chart) I have trouble just subclassing and overriding the Paint() routine because I can't figure out how to access the Storage classes from the superclass and I can't seem to access all the data required to paint just through the public API.

So, my question, stemming from my C++ ignorance: Is there a reason you make your opaque pointers 

protected: 
  ...
  class Private;
  Private* Storage;

"protected" rather than "private"? Is there some way I'm not seeing to access this->Storage from within my subclass (say, of vtkPlotParallelCoordinates) since Storage is protected? And, if not, why not just make it "private"?

Thanks for the help,
-Eric

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Eric E Monson
Duke Visualization Technology Group