The original version of Filter classes had a helper header file named
CreateResult.h that had several forms of a CreateResult function that
helped correctly create the DataSet to be returned from a filter's
DoExecute. With the move to the NewFilter structure, these functions
did not line up very well with how DataSets should actually be created.
A replacement for these functions have been added as protected helper
methods to NewFilter and NewFilterField. In addition to moving them
into the filter themselves, the behavior of CreateResult has been merged
with the map field to output functionality. The original implementation of
Filter did this mapping internally in a different step. The first design
of NewFilter required the filter implementer to call a
MapFieldsOntoOutput themselves. This new implementation wraps the
functionality of CreateResult and MapFieldsOntoOutput together so that
the DataSet will be created correctly with a single call to
CreateResult. This makes it easier to correctly create the output.