[Insight-developers] The time has come for itkTypeTraits.h?

[kent williams]

G++ 4 and later has the std::tr1 type_traits, and you can include it with
#include <tr1/type_traits> I believe.  There¹s nothing I¹ve seen in that
header that would require anything except partial template specialization.
We can¹t just glom that into ITK though, as it is licensed with some version
of GPL.

Most ‹ if not all ‹ modern compilers have some version of type_traits though
it seems like there¹s not much consistency in implementation ‹ how you get
access to them, what namespace the members are in.  I don¹t know if there¹s
a really good way to handle this, frankly.


On 11/5/10 2:19 PM, "Bradley Lowekamp" <blowekamp at mail.nih.gov> wrote:

> Kent,
> 
> One minor point is the difference between tr1 and C++0x. "std::tr1" is an
> extension to standard template library which can be implemented with the
> current C++03. C++0x includes language extensions which many are not supported
> by compilers.
> 
> So theoretically there could be an open source tr1 library someplace. Or at
> least some part of it. I think we should look at adding this extension as a
> whole instead of just a part or two.
> 
> http://en.wikipedia.org/wiki/C%2B%2B_Technical_Report_1
> 
> Brad
> 
> On Nov 5, 2010, at 3:11 PM, kent williams wrote:
> 
>> In trying to replace the use of typeids in ITK with compile-time code based
>> on Template Metaprogramming, I've run into this issue: The job would be a
>> whole lot easier if we had access to the C++0x type_traits header.
>> 
>> What would it take to make this a possibility?
>> 
>> In CMakeLists.txt:
>> 
>> CHECK_INCLUDE_FILES(type_traits HAVE_TYPE_TRAITS)
>> 
>> itkTypeTraits.h:
>> 
>> #ifndef __itkTypeTraits_h
>> #define __itkTypeTraits_h
>> #include "itkConfigure.h"
>> 
>> #if defined(HAVE_TYPE_TRAITS)
>> #include <type_traits>
>> #else
>> // implement needed type_traits macros
>> namespace std
>> {
>>   template<typename _Tp, _Tp __v>
>>     struct integral_constant
>>     {
>>       static const _Tp                      value = __v;
>>       typedef _Tp                           value_type;
>>       typedef integral_constant<_Tp, __v>   type;
>>     };
>>   typedef integral_constant<bool, true>     true_type;
>>   typedef integral_constant<bool, false>    false_type;
>> 
>> // e.g. the is_same relation
>> template<typename, typename>
>> struct is_same : public false_type { };
>> 
>> template<typename _Tp>
>> struct is_same<_Tp, _Tp>  : public true_type { };
>> 
>> }
>> #endif
>> 
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> 
> ========================================================
> 
> 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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