Though it isn't the case here, another problem with compiler template
deductions is that it won't deduce the template for template<typename T>
if the argument isn't a simple use of T. To illustrate:
this will work:
template <typename TImage>
void DoIt(const TImage *imagePtr)
{
}
typedef itk::Image<char,3> ImageType;
ImageType::Pointer iPtr;
Doit(iPtr->GetPointer()); // const ImageType *imagePtr
but this will not:
template <typename TPixel>
void DoIt(const typename itk::Image<TPixel,3> *iPtr)
{
}
typedef itk::Image<char,3> ImageType;
ImageType::Pointer iPtr;
DoIt(iPtr->GetPointer()); // asks compiler to deduce
// TPixel from ImageType::Pointer, by
way of implicit
// conversion from ImageType::Pointer to
ImageType *
// Compiler not that smart.
--
Kent Williams [email protected]
On 8/23/12 7:21 AM, "Bradley Lowekamp" <[email protected]> wrote:
>
>
>
>Hello,
>
>
>The reason you methods is not working is because C++ can't deduce the
>template parameters from the argument types passed to the function. That
>is to say since T is only used for the return type, and not as an
>argument to the function, so you should explicitly
> specify it as a template parameters. Something like this should work:
>
>
>r = this->EnableIfTest<OutputType>( 3 );
>
>
>Brad
>
>
>
>On Aug 22, 2012, at 4:08 PM, M Stauffer -V- wrote:
>
>
>Great, thanks Brad.
>
>I can reproduce what you explain below, but it's not working when I rely
>on only the return parameter type for the template parameter deduction.
>That is, the following
> won't compile
>
>template< typename T >
>typename EnableIfC< IsSame< T, ScalarDerivativeType >::Value, T >::Type
>EnableIfTest(int val)
>{
> std::cout << "Output == ScalarDerivativeType. val " << val << "\n" <<
>std::endl;
> T o;
> o.Fill(1);
> return o;
>}
>
>(and similarly with DisableIfC...)
>
>In implementation:
>
> OutputType r;
> r = this->EnableIfTest(3);
>
>I think I'll skip this for now because I have a working implementation
>and the extra overhead it has, because it requires a nested function
>call, is only a few %.
>
>I'll put up a patch soon and hopefully you could take a look at it, Brad.
>I'll let you know.
>
>-M
>
>
>
>
>
>
>________________________________________
>From: Bradley Lowekamp [mailto:[email protected]]
>
>Sent: Tuesday, August 21, 2012 3:37 PM
>To: Michael Stauffer
>Cc: [email protected]
>Subject: Re: [Insight-developers] Overloading methods
>
>
>Hello Michael,
>
>
>Here is the declaration of one of the GetComponent methods:
>
>
>template< typename T>
> typename EnableIfC<
> IsSame<T, typename NumericTraits<T>::ValueType>::Value,
> T >::Type
> GetComponent(const T pix,
> unsigned int itkNotUsed( idx ) ) const;
>
>
>
>This uses the EnableIf idom to answer lets look at a simplification of
>function:
>
>
>template< typename T> T GetComponent(const T pix, unsigned int idx )
>const;
>
>
>
>So I just simplified it some. So for function C++ has the ability to
>implicitly deduce the template parameters from the arguments passed to a
>function. So if you did the following:
>
>
>int i;
>GetComponent( i, 10 )
>
>
>C++ can deduce the template parameter T, based on the function argument i
>being of type int.
>
>
>
>
>There are a couple C++ tricks to overloading functions that should be
>considered before the EnableIf idiom should be considered. Using the
>EnableIf idom is really a last resort when simpler more understandable
>techniques can not be used.
>
>
>
>
>Brad
>
>On Aug 17, 2012, at 6:17 PM, Michael Stauffer wrote:
>
>I'm using the new EnableIfC and DisableIfC routines, to try and optimize
>itkCentralDifferenceImageFunction::Evaluate* methods by specializing for
>scalar and vector pixel types. I have it working using my own SFINAE
>method I pulled off the web. But this,
> requires calling templated subfunctions, which cost about 2% in overhead.
>
>
>
>
>
>
>Looking at itkEnableIf.h and its usage in PatchBasedDenoisingImageFilter,
>I was hoping to be able to call the specialized Evalute* methods directly.
>
>
>The method PatchBasedDenoisingImageFilter::GetComponent is are
>template-specialized to use one of two versions depending on whether the
>pixel is scalar or not. The method is templated.
>But in
>PatchBasedDenoisingImageFilter::ComputeSignedEuclideanDifferenceAndWeighte
>dSquaredNorm(), GetComponent is called without any template parameters.
>How does this work? I must be missing something.
>
>
>
>
>template
>void
>PatchBasedDenoisingImageFilter
>::ComputeSignedEuclideanDifferenceAndWeightedSquaredNorm(const PixelType&
>a, const PixelType& b,
>const RealArrayType& weight,
>bool itkNotUsed(useCachedComputations),
>SizeValueType itkNotUsed(cacheIndex),
>EigenValuesCacheType& itkNotUsed(eigenValsCache),
>EigenVectorsCacheType& itkNotUsed(eigenVecsCache),
>RealType& diff, RealArrayType& norm)
>{
>for (unsigned int pc = 0; pc < m_NumPixelComponents; ++pc)
>{
>RealValueType tmpDiff = GetComponent(b, pc) - GetComponent(a, pc);
>RealValueType tmpWeight = weight[pc];
>SetComponent(diff, pc, tmpDiff);
>norm[pc] = tmpWeight * tmpWeight * tmpDiff * tmpDiff;
>}
>}
>
>
>
>
>
>
>========================================================
>Bradley Lowekamp
>Medical Science and Computing for
>Office of High Performance Computing and Communications
>National Library of Medicine
>[email protected]
>
>
>
>
>
>
>
>
>
>
>
>
>
>========================================================
>Bradley Lowekamp
>Medical Science and Computing for
>Office of High Performance Computing and Communications
>National Library of Medicine
>[email protected]
>
>
>
>
>
>
>
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