[Insight-developers] Code/Review/itkOptImageToImageMetric strange const issues

[Luis Ibanez]

Hi Kent,

As you pointed out,
this section of code in the itkOptImageToImageMetric
class could benefit from a refactoring.

Const-correctness was enforced in this class, mostly
as an after-thought, so not all the methods are following
clean practices.

It would seem that using static_cast<> instead of the
c-style cast for (void *) should work ok.

I agree with you in the the m_Treader taking a member
variable in a non-const form should generate a compilation
error in a const method.

I'm not sure that going around silencing the warning is
the right thing to do for the long term...

May be we should reconsider some refactoring here
at some point.



          Luis

---------------------------------------------------------------------------------------
On Wed, Oct 14, 2009 at 11:38 AM, kent williams
<norman-k-williams at uiowa.edu> wrote:
> I just checked in a change to Code/Review/itkOptImageToImageMetric.txx that
> quiets a warning:
>
> Insight/Code/Review/itkOptImageToImageMetric.txx:1210: warning: cast from
> `const itk::ImageToImageMetric<itk::Image<float, 3u>, itk::Image<float, 3u>
>>::MultiThreaderParameterType*' to `void*' discards qualifiers from pointer
> target type
>
> There are 3 instances of this warning in that file.  The problem is methods
> like this:
>
> template < class TFixedImage, class TMovingImage  >
> void
> ImageToImageMetric<TFixedImage,TMovingImage>
> ::GetValueMultiThreadedPreProcessInitiate( void ) const
> {
>  this->SynchronizeTransforms();
>
>  m_Threader->SetSingleMethod(GetValueMultiThreadedPreProcess,
>                              (void *)(&m_ThreaderParameter));
>  m_Threader->SingleMethodExecute();
> }
>
> I believe the warning comes from the method being tagged as const.  This
> seems weird to me for several reasons:
>
> 1. Even if it doesn't directly modify a class member, it's passing the
> address of a class member to a second object, which may then modify it.
>
> 2. Why are we still using C-style casts?
>
> 3. Calling non-const methods on a member variable in a const class method
> constitute modifying class state -- why are the calls to SetSingleMethod not
> flagged as violations of the method's const-ness
>
> The fix I checked in addresses the warning by nesting a static_cast to const
> void * inside a const_cast to void *.  That silences the warning, but the
> whole thing looks fishy to me.
>
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