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

[Luis Ibanez]

Hi Brad,

I can't think of a drawback for the explicit constructors
right now,...  (but I may just be low in coffee).     :-/


I worry about the "invisibility" of these methods, and how
easy it is to add them, and how hard it will be to remove
them if something goes wrong with them.


I still would vote for the "CastFrom()" methods, but if
enough developers are happy with explicit constructors
and are willing to help with the maintenance of the code
for the next decade, then I'm happy to follow the crowd.   :-)


     Luis



-----------------------------------------------------------------------------
On Mon, Mar 15, 2010 at 4:03 PM, Bradley Lowekamp
<blowekamp at mail.nih.gov> wrote:
> 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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>