vtkGetConstObjectMacro for const object getters

VTK now provides vtkGetConstObjectMacro, a new macro in vtkSetGet.h that generates const getter methods for vtkObject member variables. This macro complements the existing vtkGetObjectMacro by providing const-correct access to object pointers.

Usage

The macro generates a virtual const method that returns a const pointer:

class vtkMyClass : public vtkObject
{
public:
  vtkSetObjectMacro(Points, vtkPoints);
  vtkGetConstObjectMacro(Points, vtkPoints);  // Generates: virtual const vtkPoints* GetPoints() const

protected:
  vtkPoints* Points = nullptr;
};