[Insight-developers] Casting constructors for DTI and Sym Mat pixeltypes

[Bradley Lowekamp]

Hello Luis,

Thanks for the info regarding the itk::Array, I forgot the usefulness of all the inherited methods!


In regards to this, what is the down side to using an explicit constructor? For example:

explicit 
template<TOtherValueType>
SymmetricSecondRankTensor( const SymmetricSecondRankTensor<TOtherValueType> &);

This uses standard conventions along with requiring the contractor/conversion to be explicitly defined? 

Making the following valid code:

Float3DTensorType floatTensor2(intTensor);
floatTensor2 = Float3DTensorType(intTensor);

But not:
floatTensor2 = intTensor;

Just a thought on an alternative approach....

Thanks,
Brad

p.s.
This is my understanding of C++, compilers and standards may differ :)


On Mar 15, 2010, at 3:45 PM, Luis Ibanez wrote:

> Hi Luke,
> 
> Historically we have been cautious when adding implicit
> conversions, since once that syntactic sugar is introduced
> in the code, it is very easy to get unintended consequences
> particularly when using templated code.
> 
> 
> For the case of the itkPoint we were a lot more explicit, and
> added a method:
> 
> 
> itk::Point<T>::CastFrom( const itk::Point< R > & otherPoint );
> 
> 
> See the definition in:
> 
>                   Insight/Code/Common/itkPoint.h
> 
> in lines 212-221:
> 
>  /** Copy from another Point with a different representation type.
>   *  Casting is done with C-Like rules  */
>  template < typename TCoordRepB >
>  void CastFrom( const Point<TCoordRepB,NPointDimension> & pa )
>    {
>    for(unsigned int i=0; i<NPointDimension; i++ )
>      {
>      (*this)[i] = static_cast<TCoordRep>( pa[i] );
>      }
>    }
> 
> 
> 
> I would suggest that we follow this Explicit approach for
> the Tensor classes.
> 
> 
> Would you like to give it a try at implementing and testing
> the CastFrom() methods for these classes ?
> 
> 
>  Thanks
> 
> 
>         Luis
> 
> 
> ----------------------------------------------------------------------------------
> On Fri, Mar 5, 2010 at 2:00 PM, Luke Bloy <luke.bloy at gmail.com> wrote:
>> The classes itkDiffusionTensor3D and itkSymmetricSecondRankTensor don't have
>> constructors that enable casting. ( http://www.itk.org/Bug/view.php?id=10323
>> ) so code such as the following fails.
>> 
>>  typedef itk::SymmetricSecondRankTensor<int,3>     Int3DTensorType;
>>  typedef itk::SymmetricSecondRankTensor<float,3>   Float3DTensorType;
>>  typedef itk::SymmetricSecondRankTensor<double,3>  Double3DTensorType;
>>  Int3DTensorType intTensor(1);
>> 
>>  //Test constructors
>>  Float3DTensorType floatTensor(intTensor);
>>  Double3DTensorType doubleTensor(floatTensor);
>> 
>>  //test Assignment
>>  Float3DTensorType floatTensor2 = intTensor;
>> 
>> 
>> adding templated constructors and assignment operators will allow this type
>> of behavior.
>> 
>> Is there a reason these constructors have been not been defined?
>> 
>> -Luke
>> 
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> _______________________________________________
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> 
> Visit other Kitware open-source projects at
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> 
> Kitware offers ITK Training Courses, for more information visit:
> http://kitware.com/products/protraining.html
> 
> Please keep messages on-topic and check the ITK FAQ at:
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