Re: [boost] [Range] patched: boost/range/iterator.hpp

From: Thorsten Ottosen (thorsten.ottosen_at_[hidden])
Date: 2006-05-09 11:26:54

David Abrahams wrote:

 > Thorsten Ottosen <thorsten.ottosen_at_[hidden]> writes:
 >
 >
 >> In the new version, this is how range_iterator is defined:
 >>
 >> namespace boost
 >> {
 >>     template< typename C >
 >>     struct range_iterator
 >>     {
 >>         typedef BOOST_RANGE_DEDUCED_TYPENAME
 >>             mpl::if_< BOOST_DEDUCED_TYPENAME is_const<C>::type,
 >>                       BOOST_DEDUCED_TYPENAME range_const_iterator<
 >>                           BOOST_DEDUCED_TYPENAME 
remove_const<C>::type >::type,
 >>                       BOOST_DEDUCED_TYPENAME 
range_mutable_iterator<C>::type >::
 >> type type;
 >>     };
 >>
 >> } // namespace boost
 >
 >
 >
 > Well, I think the logic is probably right but I have to say the code
 > looks a lot more complex than it probably ought to.

I think I can remove some partial specializations based on constness, 
like you suggested, eg.:

template< class R >
const_iterator<R const> : const_iterator<R>
{ };

But besides that, what else do you think looks complicated?

(Constness has certainly been a major pain)

 > There are lots of
 > places where the current code could profit from refactoring; this
 > might be another such place.  For example, if you make range_iterator
 > do the right thing always, (maybe) you could spell
 > range_const_iterator as follows:
 >
 >   template <class T>
 >   struct range_const_iterator
 >     : range_iterator<T const>
 >   {};
 >
 > It's just an example; you have to check it to make sure it works out.
 > Anyway, I suggest you look hard for simplifying refactorings before
 > you commit a big rewrite.

I the new design, range_iterator depends on two other traits:

- range_mutable_iterator
- range_const_iterator

your suggestion would make the design circular dependent.

-Thorsten