PODs vs memset

[Paolo Carlini <pcarlini at suse dot de>]

Hi everyone, hi Gaby,

while quickly adapting valarray to use the front-end __is_pod instead of 
the library version (otherwise it didn't compile), I adjusted this code 
in valarray:

 template<typename _Tp>
   struct _Array_default_ctor<_Tp, true>
   {
     // For fundamental types, it suffices to say 'memset()'
     inline static void
     _S_do_it(_Tp* __restrict__ __b, _Tp* __restrict__ __e)
     { std::memset(__b, 0, (__e - __b) * sizeof(_Tp)); }
   };

 template<typename _Tp>
   inline void
   __valarray_default_construct(_Tp* __restrict__ __b, _Tp* 
__restrict__ __e)
   {
     _Array_default_ctor<_Tp, __is_pod(_Tp)>::_S_do_it(__b, __e);
   }

I think you (Gaby) made sure the latter scheme worked fine with the message:

   http://gcc.gnu.org/ml/gcc/2005-12/msg00266.html

Now however the problem is that __is_pod actually establishes POD-ness, 
not just a weak subset of it (basically only scalars), therefore wanted 
to double check with you that the positive result of that thread also 
holds for all POD types. Depending on the answer I will either:

   1- To be safe, change valarray to use a library-based __is_scalar or 
whatelse you would suggest.
   2- Do not further change valarray and instead think about improving 
stl_algobase.h / stl_uninitialized.h / maybe the containers (I have to 
see) consistently with the above, thus always using memset (zero) for  
default-construction of POD types.

Thanks,
Paolo.