[vtk-developers] Proposal for array classes

[David C Thompson]

Hi all,

	I would like to propose adding a vtkInformation pointer to the
vtkAbstractArray class. It need not be allocated at construction, simply
publicly accessible:

class vtkAbstractArray : public vtkObject
{
public:
  // ...
  vtkSetObjectMacro(Information,vtkInformation);
  vtkGetObjectMacro(Information,vtkInformation);
  // ...
protected:
  vtkInformation* Information;
};

I can think of several uses:

1. storing units associated with values in an array;

2. keeping/suggesting a window (which need not be the same as the data
range -- it might be a superset of the range if data is being streamed
or handled in parallel or a subset if used for feature tracking) used
when rendering scalars as colors;

3. annotating the components of an array (i.e., storing a string naming
each component in addition to the name of the array as a whole -- which
should be of increasing use as VTK is used for information
visualization); and

4. storing summary statistics (mean, variance, ...) of array values.

I know that vtkAbstractArray should be kept as lightweight as possible
since many instances of its subclasses are typically in use at the same
time. However, this should only add 4-8 bytes. For reference, these are
the sizes of vtkAbstractArray and some descendants on my 64-bit machine:

sizeof(vtkAbstractArray):    64 bytes
sizeof(vtkStringArray):      80 bytes
sizeof(vtkDataArray):       352 bytes
sizeof(vtkDoubleArray):     384 bytes

As far as operations go, only one initialization (to zero the pointer)
in the constructor and one branch + function call (to delete the
information object) in the destructor would be required.

Does anyone have any thoughts/objections? Especially someone at Kitware
who has the authority to say yea or nay?

	Thanks,
	David