[Insight-developers] Integrating the New Statistics framework into ITK

[Karthik Krishnan]

I forgot to mention the reason for giving you 2 options. I've tried to weigh
both the options below :

Option A  vs B
---------------------

1. Code duplication:

    With A, if a file remains unchanged, it has to be duplicated
    (and maintained, at least as long as Bill is around) in both
    directories.

    With B, we have to worry only about the classes which need
    refactoring. Even refactoried files, where changes are minimal,
    you can even code of the form:

      namespace Statistics{
        class Blah {
           #ifdef ITK_USE_DEPRECATED_STAT
              void SetInputSample( ListSampleType * );
           #else
              void SetInput( ListSampleType * );
           #endif
         }
       }


2. Code separation and readability

    A separates the classes clearly in two directories. The statistics
    library will be devoid of ugly ifdefs. If we decide to drop the
    deprecated version at some point, we simply have to terminate
    a directory.

    We can do the same with Option B, in a less obvious way, by
    separating the classes in two files, for instance :

      File StatistiitkSample.h:
         #include "StatisticsDeprecated/itkSample.h"
         #include "StatisticsNew/itkSample.h"

      File StatisticsDeprecated/itkSample.h
         namespace StatisticsDeprecated
          {
          class Sample : public Object { ... }
          }

      File StatisticsNew/itkSample.h
         namespace StatisticsNew
          {
          class Sample : public DataObject { ... }
          }


3. Surprises

  With A there are no surprises. I suspect that with B, using
  anonymized namespaces etc, in several translation units,
  some compiler might scream ? I tried to verify it with minimal
  C++ code on gcc4.3, but I feel uneasy about it.


Please let us know your thoughts.
Regards
--
karthik

On Sat, Apr 4, 2009 at 11:57 AM, Karthik Krishnan <
karthik.krishnan at kitware.com> wrote:

> Hello:
>
> As you may know, the ITK statistics framework have been revamped. The new
> framework follows ITK pipeline mechanics, removes redundant classes and
> provides a consistent API. The new classes are not backwards compatible. For
> details, please visit
>
>
> http://www.itk.org/Wiki/Proposals:Refactoring_Statistics_Framework_2007_Migration_Users_Guide
>
> We would like to integrate the new statistics framework into ITK. Given
> that there are numerous API changes, to keep things backward compatible, we
> are considering taking one of the following approaches :
>
>
> --------------
> Option A
>
> - Rename the existing Statistics/ directory in ITK to StatisticsDeprecated/
>
> - Create a parallel directory Statistics/ containing the new classes.
>
> - Add an ITK_USE_DEPRECATED_STATITSTICS_FRAMEWORK option at configure time
> to toggle between the usage of the deprecated and the new framework. The
> option will cause (a) the right directory to be compiled (b) headers from
> there right directory to be installed (c) the right directory to be added to
> the include dirs.
>
> - All existing code in the toolkit using the statistics framework will be
> ifdef'ed to work with both the new and the old framework. For instance :
>
> #ifdef ITK_USE_DEPRECATED_STATISTICS_FRAMEWORK
>   calculator = Statistics::CovarianceCalculator< ListSampleType >::New();
>   calculator->SetInputSample(sample);
>   calculator->Update();
> #else
>   filter = Statistics::CovarianceFilter< ListSampleType >::New();
>   filter->SetInput( sampleGenerator->GetOutput() );
>   filter->Update();
> #endif
>
>
> --------------------------------------------------
>
> Option B
>
> - Keep all files in a single directory but use two different namespaces.
>
> For instance the file itkSample.h would look like :
>
> namespace itk
>   {
>   namespace StatisticsDeprecated
>     {
>     class Sample : public Object { ... }
>     }
>
>   namespace StatisticsNew
>     {
>     class Sample : public DataObject { ... }
>     }
>   }
>
> - The ITK_USE_DEPRECATED_STATITSTICS_FRAMEWORK option redefines the unused
> namespace to be an anonymous namespace. The used namespace to "Statistics".
> For instance :
>
>   #ifdef ITK_USE_DEPRECATED_STATITSTICS_FRAMEWORK
>     #define StatisticsDeprecated Statistics
>     #define StatisticsNew
>   #else
>     #define StatisticsNew Statistics
>     #define StatisticsDeprecated
>   #endif
>
> User code still looks the same :
>
> #ifdef ITK_USE_DEPRECATED_STATISTICS_FRAMEWORK
>   calculator = Statistics::CovarianceCalculator< ListSampleType >::New();
>   calculator->SetInputSample(sample);
>   calculator->Update();
> #else
>   filter = Statistics::CovarianceFilter< ListSampleType >::New();
>   filter->SetInput( sampleGenerator->GetOutput() );
>   filter->Update();
> #endif
>
> -----------------------------------------
>
> Any thoughts the developers have on this issue.
>
> We have gathered a wikipage to assemble ideas:
>   http://www.itk.org/Wiki/Proposals:Refactoring_Statistics_Framework_2007
>
> The refactored code is in the NAMIC sandbox.
>
>
>
> Thanks
> Regards
>
> --
> Karthik Krishnan
> R&D Engineer,
> Kitware Inc.
> Ph: 518 881 4919
> Fax: 518 371 4573
>



-- 
Karthik Krishnan
R&D Engineer,
Kitware Inc.
Ph: 518 881 4919
Fax: 518 371 4573
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