[Insight-users] itk::SmartPointer - problem making code const-correct

[Luis Ibanez]

Hi Frederic,


The function:

     template<typename TITKImgType>
     bool
     WriteFile(
         const std::string& a_fullFilename,
         typename TITKImgType::ConstPointer);

will be better written as

     template<typename TITKImgType>
     bool
     WriteFile(
         const std::string& a_fullFilename,
         const TITKImgType * );


and you will be able to call it as

    ImgType::Pointer image = filter->GetOutput();

    WriteFile<ImgType>("out.mhd", image );



(not need to use "GetPointer()" in this case)


Normally you don't need to call GetPointer() in ITK.



Regards,


      Luis


-------------------------------------------------------------------------
On Fri, May 28, 2010 at 4:32 AM, Frederic Perez <fredericpcx at gmail.com>wrote:

> Hello Stuart,
>
> I would like to be able to do those kinds of assignments too!
>
> For example, in our group we have functions like this one:
>
>      template<typename TITKImgType>
>      bool
>      WriteFile(
>          const std::string& a_fullFilename,
>          typename TITKImgType::ConstPointer);
>
> declared this way to promise that WriteFile won't modify the input image.
> (By the way, the template stuff is not relevant to this thread.)
>
> In order to workaround the const-vs-nonconst problem, we do calls like
> this:
>
> typedef itk::Image<int, 3> ImgType;
> ImgType::Pointer image = ImgType::New();
> ...
> WriteFile<ImgType>("out.mhd", image.GetPointer());
>
> Unfortunately, this populates the code with lots of GetPointer() that we
> would like to get rid of.
> Not a real solution, but maybe you can use it.
>
> I would like to hear more on this issue.
>
> Cheers,
>
> Frederic Perez
>
> On Thu, May 27, 2010 at 7:21 PM, Stuart Golodetz <itk at gxstudios.net>wrote:
>
>>  Hi,
>>
>> Hope this is the right place to post this. I was just wondering if
>> there's a reason why itk::SmartPointer was designed so as not to allow e.g.
>>
>> itk::Image<int,3>::Pointer image;
>> const itk::Image<int,3>::ConstPointer& cimage = image;
>>
>> ?
>>
>> The equivalent with boost::shared_ptr is allowed, e.g.
>>
>> boost::shared_ptr<int> p(new int);
>> const boost::shared_ptr<const int>& cp = p;
>>
>> This doesn't seem like a major problem, until you start writing
>> functions taking const itk::Image<...>::ConstPointer& parameters - at
>> which point it won't let you pass a normal Pointer in without explicitly
>> constructing a ConstPointer from it. Now the types are often quite long,
>> and it's annoying to have to add extra typedefs in the calling code just
>> for that purpose. Duplicating the functions with const
>> itk::Image<...>::Pointer& parameters doesn't work either, because you
>> get a combinatorial explosion when you have multiple such parameters.
>> For instance, with 3 parameters, you have to create functions with
>> combinations:
>>
>> const Pointer&, const Pointer&, const Pointer&
>> const Pointer&, const Pointer&, const constPointer&
>> const Pointer&, const ConstPointer& const Pointer&
>> // more here
>> const ConstPointer&, const ConstPointer& const ConstPointer&
>>
>> This seems like an unproductive way to spend one's time, to say the
>> least. The only other "reasonable" alternative I've managed to come up
>> with that doesn't either (a) clutter up the call site or (b) cause the
>> combinatorial explosion just outlined, is to just use the non-const
>> Pointers everywhere and abandon the idea of making the code
>> const-correct. But that seems defeatist to me  :)  Please could you tell
>> me if there's something I'm missing? (And if so, what?)
>>
>> Cheers,
>> Stuart
>>
>>
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>
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>
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> http://www.kitware.com/products/protraining.html
>
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