Re: Simulating Partial Specialization

From: Boris Fomitchev (fbp_at_[hidden])
Date: 2000-10-02 10:45:54

Looks like ISPTR used as a discriminator for full class
specialization  
will work if ISCONST used as a secondary discriminator and member 
template classes work :

template <bool is_ptr, bool is_const>
struct iterator_traits_helper
{
  template <class Iterator> class iterator_traits_base {
    typedef typename Iterator::value_type value_type;
    ...
  }
};

template<>
struct iterator_traits_helper<true, true>
{
  // we know for sure this guy is const T*
  // remove_const template is supposed to remove const -- do we have 
that ???
  template <class Iterator> class iterator_traits_base {
    typedef typename remove_const<Iterator>::value_type value_type;
    ...
  }
}; 

template <class T>
struct iterator_traits : public 
iterator_traits_helper::iterator_traits_base<IS_PTR<T>::Ret, 
IS_CONST<T> > {
};

The problem might be that VC6 might not work very well with typedefs 
inside member template classes...

-Boris.
--- In boost_at_[hidden], jbandela_at_u... wrote:
> Anybody have any ideas of how to use this technique to implement 
> iterator_traits in the STL? This technique allows differentiation 
> between user defined iterators and pointers as iterators. Does 
> anybody know of any technique that can allow value_type to be 
> specified. (The only way I can think to do this would be with the 
non-
> existant typeof).
> 
> Regards,
> 
> John R. Bandela