Gabriel Dos Reis <gdr@integrable-solutions.net> writes:
David Abrahams <dave@boost-consulting.com> writes:
| Daniel Frey <daniel.frey@aixigo.de> writes: | | > Consider: | > | > // A strange way to retrieve my_container.begin(): | > boost::prior( my_container.end(), my_container.size() ); | > | > Is that legal? The second template parameter of boost::prior is | > deduced to an unsigned(!) type, which IMHO means that -n is undefined, | > right? Do we need to fix this? Maybe: | > | > template <class T> | > T prior(T x, typename T::difference_type n) | > { | > std::advance(x, -n); | > return x; | > } | | Well, that wouldn't work! | How would you call prior(p, 4) when p is int*?
I suppose he wanted to say
template<class T> T prior(T x, typename std::iterator_traits<T>::different_type n)
?
| > or shall we document that it's illegal/undefined to call | > boost::prior() with an unsigned second parameter? | | Hmm, no I think if it's unsigned we should either deduce an | appropriate signed type or implement the "backward advance" | ourselves. We could use reverse_iterator to do that, FWIW.
That would be an isomorphic implementation, indeed.
Hey! These implementations using "advance" don't work for non-iterators (e.g. int) the way regular next() and prior() do. I consider this a bug! -- Dave Abrahams Boost Consulting www.boost-consulting.com