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::ComputeSignedEuclideanDifferenceAndWeightedSquaredNorm(),
>> 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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