On 27. Nov 2019, at 15:55, Zach Laine via Boost <boost@lists.boost.org> wrote:
On Wed, Nov 27, 2019 at 8:38 AM Andrzej Krzemienski via Boost < boost@lists.boost.org> wrote:
For non-contiguous random_access_iterators (like in deque) it might be suboptimal to do it this way: a directly provided operator== might be faster than the one synthesized from operator-. Of course, I can provide the 6 relops operators myself, but I could have only 2 if the facade were capable of generating operator!= from operator== (and similar). Could operator!= for random_access_iterator be generated from operator!= ?
It's true that the deque case will be suboptimal. Here are my considerations though:
- The point of the library is to reduce the amount of code you must write to the bare minimum, and basing all the relops on op- and op== does not serve that goal. - Any generated operation (not just the relops) can be replaced by the user at will, just be having the user define that operation. In the deque case, that means defining op-, op==, and op!=. Deque is not the common case -- most random-access containers are also contiguous. I want to maintain the brevity of the common case. That means the solution is clear documentation, IMO.
I think Andrzej made a good point, it should be possible to override automatically generated operators by adding a minimal number of extra operators, minimal demo: https://godbolt.org/z/zaFpBU