Re: Make sorting stable

On 04.03.2020 at 19:11, Nikita Popov wrote: > 1. As Tyson suggests, we can throw a warning if a boolean is returned from > the comparison callback (probably with a check to only throw it once per > sort), to make it obvious what the cause is. > > 2. We can fix this transparently by doing something like this internally: > > $result = $compare($a, $b); > if ($result !== false) { > return (int) $result; // Normal behavior > } > > // Bad comparison function, try the reverse order as well > return -$compare($b, $a); > > That is, we will recover the full three-way comparison result from the > "greater than" result, by checking for both $a > $b and $b > $a. 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#L372> -- Christoph M. Becker