[Insight-developers] Advice needed from C++ Template wizards.

[kent williams]

I'm trying to fix this bug:
http://public.kitware.com/Bug/view.php?id=3610

the problem is this code:

  typename TFeatureImageType::Pointer tempFeature;
  if ( typeid(TImageType) == typeid(TFeatureImageType))
    {
    m_Canny->SetInput(tempFeature);
    }
  else
    {
    m_Caster->SetInput(tempFeature);
    m_Canny->SetInput(m_Caster->GetOutput());
    }

This code breaks if typeid(TImageType) != typeid(TFeatureImageType), since
the compiler still compiles the top branch of the if statement, and the
m_Canny->SetInput() call will be in error because of incorrect parameter
type.

I thought I could fix this with specialization, like this:
> // IN CLASS DEFINITION
> template <class _TImageType, class _TFeatureImageType>
> void AssignCannyInput(typename _TFeatureImageType::Pointer &input)
> {
>   m_Caster->SetInput(input);
>   m_Canny->SetInput(m_Caster->GetOutput());
> }
> template <>
> void AssignCannyInput<TImageType,TImageType>(typename TImageType::Pointer
> &input)
> {
>   m_Canny->SetInput(input);
> }

But the compiler objects to the specialization inside the class definition,
and moving the specialization out of the class like this:

> // Removed from class definition, moved to TXX file
> template< class TImageType, class TFeatureImageType >
> template <>
> void
> CannySegmentationLevelSetFunction< TImageType, TFeatureImageType >
> ::AssignCannyInput<TImageType,TImageType>
> (typename TImageType::Pointer &input)
> {
>   m_Canny->SetInput(input);
> }

Is illegal as well.

Does anyone know of a good Template MetaProgramming solution to this issue?

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