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

From: David Abrahams (dave_at_[hidden])
Date: 2006-05-10 15:23:02

Thorsten Ottosen <thorsten.ottosen_at_[hidden]> writes:

> 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?

Maybe it's just all the macros.  BOOST_DEDUCED_TYPENAME should have
been renamed BOOST_TYPENAME years ago, but you're still using it way
more than I've ever found necessary to satisfy old compilers.

> (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.

Well of course I wasn't suggesting circularity.

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com