Re: Make sorting stable

On Wed, Mar 4, 2020 at 12:12 PM Nikita Popov <nikita.ppv@gmail.com> wrote: > On Wed, Mar 4, 2020 at 6:17 PM Sara Golemon <pollita@php.net> wrote: > >> On Wed, Mar 4, 2020 at 10:42 AM Nikita Popov <nikita.ppv@gmail.com> >> wrote: >> >>> The only issue I ran into is that this change has a negative impact on >>> code >>> using illegal comparison callbacks like this: >>> >>> usort($array, function($a, $b) { >>> return $a > $b; >>> }); >>> >>> Let's define what "negative impact" means in this regard. Is it that >> one still winds up with an essentially sorted array, but hitherto "stable >> appering" output is now stable in a different way? Or is the result >> actually just NOT sorted in a way that a reasonable user would consider >> correct (e.g. 5 sorted before "3")? >> > > "Negative impact" is PR speak for "completely broken" ;) Yes, it could > sort 5 before 3. The comparison function becomes completely ill-defined and > you get Garbage-In-Garbage-Out. > > Roger that, thanks for explaining. 👍 > If we are concerned about this (I'm not sure we should be, but I've at > least seen people be interested about this peculiar behavior: > > https://stackoverflow.com/questions/59908195/how-come-usort-php-works-even-when-not-returning-integers), > there's two things we can do: > > 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); > > ¿Por que no los dos? Fixing broken stuff transparently for a smooth upgrade path PLUS letting people know they're doing it wrong seems win-win and low cost. -Sara