David Abrahams wrote:
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*?
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.
template <class T> T prior(T x, ptrdiff_t n) would be fine (waves hand) if you ask me. (Blasphemy!! Burn him!)