[Insight-developers] finding/using type_traits facility from C++0x?

[Bradley Lowekamp]

I like Gaetan's approach the best. It should also be the simplest to implement as it just uses member function overloading, and doesn't needed additional classes or infrastructure. The compiler should choose the non-templated member function before the templated one.

Brad


On Oct 27, 2010, at 11:27 AM, kent williams wrote:

> Having investigated this, and looked at Tom V’s version, I have this implementation question:
> 
> To use the standard type_traits template metaprogramming facility, you have to include type_traits.
> 
> Apparently in the latest Visual C++, type_traits is a standard include, and the is_same class test is in the std:: namespace.
> If you’re using GCC 4.x.x, the header is in the tr1 subdirectory and the is_same test is in the std::tr1:: namespace.
> Any other compiler, who knows?
> 
> I added a test for type_traits in the top-level CMakeLists.txt and on OS X it isn’t found, because the tr1 include directory isn’t in the system include path.
> 
> Should I assume C++0x is too new to mess with and use my own version of the is_same type test, or should I try and come up with a comprehensive way to find type_traits or punt and define my own is_same test?
> 
> 
> 
> On 10/26/10 12:16 PM, "Bradley Lowekamp" <blowekamp at mail.nih.gov> wrote:
> 
>> Hello Kent,
>> 
>> This is a lot easier now that we can use partial template specialization. This reminds me of the common IsSameType construct (which you tried something very similar with a function):
>> 
>>  /// generic programming to test if T is the same type as U 
>>     template <typename T, typename U> 
>>     struct IsSameType {
>>       /// true if T is the same type as U 
>>       static const bool result = false;
>>     };
>>     
>>     
>>     /// generic programming to test if T is the same type as U 
>>     template <typename T>
>>     struct IsSameType<T,T> {
>>       /// true if T is the same type as U 
>>       static const bool result = true;
>>     };
>> 
>> 
>> One way to address this is to define a class in the member function or as a member of class. I believe you can do the needed partial specialization in both of these scopes. Then just add a member function to the above construct that is specific to that specialization. 
>> 
>> This is what I would try... not 100% it'll work though.
>> 
>> Good luck,
>> Brad
>> 
>> On Oct 26, 2010, at 12:36 PM, kent williams wrote:
>> 
>>> 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?
>>> <ATT00001..txt>
>> 
>> ========================================================
>> 
>> Bradley Lowekamp 
>> 
>> Lockheed Martin Contractor for
>> 
>> Office of High Performance Computing and Communications
>> 
>> National Library of Medicine 
>> 
>> blowekamp at mail.nih.gov
>> 
>> 
>> 

========================================================
Bradley Lowekamp  
Lockheed Martin Contractor for
Office of High Performance Computing and Communications
National Library of Medicine 
blowekamp at mail.nih.gov


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