[boost] Re: Simulating Partial Specialization

From: Mat Marcus (mmarcus_at_[hidden])
Date: 2000-10-02 12:59:25

>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...

It looks like you have rediscovered the metactrl::IF technique. 
However the problem of determining the underlying type from a pointer 
template parameter at compile time remains unsolved AFAIK.

- Mat