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

Raoul Gough writes:

David Abrahams writes:

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Raoul Gough writes: [snip]

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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; };

I don't see why that's preferable to what we have now with referent.

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

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

Yes to the latter; you can read all about it in the new iterator adaptor / facade / concepts documents. Also see std::vector<bool>::iterator. -- Dave Abrahams Boost Consulting www.boost-consulting.com