[Insight-developers] ConstPointers

[Mark Foskey]

Luis Ibanez wrote:

> 
> Hi Mark,
> 
> You are right,
> 
> This is an inconsistency problem that should be fixed.
> It goes back to a year ago when we started enforcing
> const-correctness on the "GetInput()" methods but didn't
> go all the way down to include the GetOutput() methods.
> 
> 
> The recipient of the filter->GetOutput() shouldn't be
> allowed to modify the image. That will break the
> consistency of the pipeline.
> 
> We could fix most of them by changing
> 
>              itkImageSource.h
> 
> where
> 
>   OutputImageType * GetOutput(void);
>   OutputImageType * GetOutput(unsigned int idx);
> 
> should be
> 
>   const OutputImageType * GetOutput(void) const;
>   const OutputImageType * GetOutput(unsigned int idx) const;
> 
> Most of the image filters inherit their GetOutput()
> method from this itkImageSource class.
> 
> 
> About the second assignment that you describe,
> this seems to be something to fix on the SmartPointer
> class itself. I would expect the declaration:
> 
>    SmartPointer &operator = (ObjectType *r)
> 
> in itkSmartPointer.h line 129 to take care of
> the const case when SmartPointer is instantiated
> over "const Self"...

You are correct.  There was a different error in my declaration that 
actually caused the problem.  Sorry about that.

> 
> All filters should take "const input images"
> as input, since a filter is not supposed to
> modify its inputs, just read data from them.
> 
> 
> 
> 
>   Luis
> 
> 
> 
> ---------------------
> Mark Foskey wrote:
> 
>> There is what appears to be an inconsistency with SmartPointers and 
>> const-ness.  You can do:
>>
>>   ImageType* image = someFilter->GetOutput();
>>   ImageType::Pointer imageSmart = image;
>>
>> But you cannot do:
>>
>>   const ImageType* image = someFilter->GetOutput();
>>   ImageType::ConstPointer imageSmart = image;
>>
>> Or at least, I can't do it with MSVC 6.0.  There is no operator=() 
>> defined for that case.
>>
>> I believe this has never come up because you rarely take a const image 
>> as input since you might want to call its Update() method.  Perhaps we 
>> should explicitly point that out to people trying to write filters.
>>
>> Is this inconsistency a problem that should be fixed?
>>
> 
> 
> 

-- 
Mark Foskey    (919) 843-5436  Computer-Aided Diagnosis and Display Lab
mark_foskey at unc . edu            Department of Radiology, CB 7515, UNC
http://www . cs . unc . edu/~foskey  Chapel Hill, NC  27599-7515