[Insight-developers] itkStaticConstMacro and Explicit Instantiation

[Brad King]

Jim,

I've been trying to introduce explicit instantiations in my working copy 
of ITK, but I've run into a problem with itkStaticConstMacro.  This 
example demonstrates the problem:

template <int N>
struct A
{
   static const unsigned int D = N;
   typedef A<D> Self;
};

extern template struct A<2>;

When compiling with GCC 3.3, the compiler is walking through the 
declarations of A<2> and marking them as do-not-instantiate.  When it 
gets to the typedef, it needs to access the definition of "D", but it is 
not allowed to instantiate D and complains.  If I replace the 
declaration of D with an enumeration, it works.

If I remember correctly, we need the StaticConstMacro only because 
Borland does not support using an enumeration.  Since Borland does not 
support extern template anyway, I propose that we change the macro to 
use enum everywhere but borland.

Comments?
-Brad