Re: indirect_iterator_generator<list<shared_ptr<X> >::iterator> again

From: Raoul Gough (yg-boost-users_at_[hidden])
Date: 2003-07-17 04:32:30

David Abrahams <dave_at_[hidden]> writes:

> Raoul Gough <yg-boost-users_at_[hidden]> writes:
[snip]
>> Really seems a bit weird that boost::referent wasn't already
>> invented in the type_traits portion of the library, since it can be
>> applied to any kind of pointer, iterator, etc... Anyway, it has
>> neatened up my code quite a bit, thanks.
>
> It's a little quirky, yet.  If you define an iterator with a nested
> element_type member it will do the wrong thing.

I guess in an ideal world, we would have something like this:

template<typename T> struct handle_traits {
  typedef typename T::value_type value_type;
  typedef typename T::pointer_type pointer_type;
  typedef typename T::reference_type reference_type;
};

template<typename T> struct iterator_traits : public handle_traits<T> {
  typedef typename T::iterator_category iterator_category;
  typedef typename T::difference_type difference_type;
};

Since an iterator is-a handle with additional functionality
(i.e. movability to one extent or another). In the case of
indirect_iterator<T>, we would need valid instantiations for
iterator_traits<T> and handle_traits<iterator_traits<T>::value_type>

BTW, does it ever make sense to have pointer_type != (value_type *) or
reference_type != (value_type &) ??

-- 
Raoul Gough
"Let there be one measure for wine throughout our kingdom, and one
measure for ale, and one measure for corn" - Magna Carta