[Insight-developers] Templated itk::Math floating point to integer proposal

[Bradley Lowekamp]

Hello Tom,

	I am going to open my mouth one more time on this issue. Hopefully I  
am being helpful :)


On Jul 27, 2009, at 12:53 PM, Tom Vercauteren wrote:

> Hi all,
>
> The only problem with this solution is that we cannot reuse the same
> name because:
>
> 1) replacing
>  int  itk::Math::Round( double x )
> by
>  template <typename TReturn>
>  TReturn itk::Math::Round( double x)
> would break backward compatibility
>
> 2) Using a default template argument is not an option since this is
> not allowed by the standard (see e.g.
> http://codeidol.com/cpp/cpp-templates/Future-Directions/Default-Function-Template-Arguments/)
>

I did not know it wasn't standard. At least the article says that for  
our case it as would be a useful feature.

Can the template and non-template version co-exist? Isn't this just a  
form of function overloading? (my gcc compiler will allow this)

Do we have to replace?

>
> My current approach is to leave the current functions as is and add a
> templated version of them. They are prepended by a capital T, e.g.
>  template <typename TReturn>
>  TReturn itk::Math::TRound( double x)

I would still think that we should surround the old Round method with  
"#ifndef ITK_LEGACY_REMOVE" because this will help to track down all  
usages, and make sure we get the right type. It will also prevent the  
wrong methods from being used again.

>
> If anyone has a better proposal, I'll be glad to hear.
>
> The following patch
>  http://www.itk.org/Bug/file_download.php?file_id=2383&type=bug
> implements that proposal but there are a few things I would like to
> get feedback on:
>
> 1) I chose to put the new code in a new file (Code/Common/itkMath.h)
> and remove the itk::Math code from itkMacro.h. itkMacro.h includes
> tkMath.h for backward compatibility

Sounds good.

>
> 2) I have added a itk::Math::Detail namespace within itk::Math to put
> helper functions that should not be used by end-users but need to be
> in the header file to be potentially inlined
>
> 3) I chose not to directly rely on the functions from vnl_math.h to
> ease the process of writting and modifying these functions


It would be nice if we could add that "Detail" namespaces are excluded  
from Backwards compatibility policy.

>

>
> 4) My helper functions rely on vxl_int_64 and  vxl_int_32 as a hope to
> get a portable fixed-width integer within ITK

Excellent!

>
>
> Also, I am not sure if it's still time to commit something like that.
> There is no release schedule for 3.16
>  http://www.vtk.org/Wiki/ITK_Release_Schedule
> But if we are close to the feature freeze, I'll definitely hold on
> before moving on.

Luis?

>
> Regards,
> Tom

========================================================
Bradley Lowekamp
Lockheed Martin Contractor for
Office of High Performance Computing and Communications
National Library of Medicine
blowekamp at mail.nih.gov


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