Re: Make sorting stable

On 05.03.2020 at 13:05, Nikita Popov wrote: >> Given that we have internal classes which deliberately have such >> comparison behavior (i.e. returning 0 or 1, to signal that there is no >> order defined), e.g. Closures[1], I tend to prefer raising a warning >> instead of trying to recover. >> >> [1] >> >> <https://github.com/php/php-src/blob/php-7.4.3/Zend/zend_closures.c#L372ƒ‚5¥‚Ïic†“S¼ >> K> > > This is a different case. The problem with my example is that it reports > equality where none exists, which is an issue if you try to change the > ordering of equal elements. Your case (which is indeed somewhat common in > extension code) always returns "greater-than" for non-equal elements. The > end result here is that the sort will not have any defined order regardless > of how we perform it. We can't really do anything about such cases. Oops, of course. Thanks for clarifying! :) > I expect that a proposal for userland compare and equality overloading may > want to make the "not ordered" case more explicit, in which case we could > throw a warning when such comparisons are performed as part of sorting. ACK. -- Christoph M. Becker