"Neal D. Becker" <ndbecker2@verizon.net> writes:
David Abrahams wrote:
"Neal D. Becker" <ndbecker2@verizon.net> writes:
Is the preference for the former case over the latter intentional?
Not particularly; it just worked out that way. I guess in the interest of efficiency it'd be better to take the one that doesn't involve a unary minus.
This caused some surprise when I tried to re-implement my cycle_iterator_adapator (a kind of circular buffer adaptor).
std::copy (b, a, ...) will do: template<typename _RandomAccessIter, typename _OutputIter> inline _OutputIter __copy(_RandomAccessIter __first, _RandomAccessIter __last, _OutputIter __result, random_access_iterator_tag) { typedef typename iterator_traits<_RandomAccessIter>::difference_type _Distance; for (_Distance __n = __last - __first; __n > 0; --__n) { *__result = *__first; ++__first; ++__result; } return __result; }
As I implemented cycle_iterator_adaptor distance_to, it was expecting that given iterators [a,b], you probably want a positive distance from a to b,
Correct, if b is reachable by applying increments to a.
but the way iterator_adaptors is implemented, it wants a negative distance.
Huh? What do you mean "it wants"?
Sorry for the confusion. I'm implementing a kind of circular buffer. You can reach from a->b or b->a with a positive increment.
Whoa there. A circular buffer must always have one invalid element. Reaching a->b->a with positive increments should be impossible, or you have a bug in your implementation. At least, that was true the last time I thought about it. Otherwise, how can you tell the difference between empty and full? -- Dave Abrahams Boost Consulting http://www.boost-consulting.com