On Wed, Mar 4, 2020, at 12:35 PM, Sara Golemon wrote:
> On Wed, Mar 4, 2020 at 12:12 PM Nikita Popov <nikita....@gmail.com> wrote:
>
> > On Wed, Mar 4, 2020 at 6:17 PM Sara Golemon <poll...@php.net> wrote:
> >
> >> On Wed, Mar 4, 2020 at 10:42 AM Nikita Popov <nikita....@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
I concur. If a comparison function returns a non-legal value:
1) Fold it to a legal value. if feasible.
2) Raise a notice/warning, maybe deprecated? that tells them they're Doing It
Wrong(tm)
3) Sometime in the future turn that notice/warning into a hard error.
If I'm understanding the definition of stable here, it means that if two values
evaluate to equal they will always end up in the same order in the output that
they were in the input, yes? So (trivial example):
$a = ["3", 2, 3, 5];
Sorts to:
[2, "3", 3, 5];
always, whereas right now it may sort to that or to [2, 3, "3", 5], somewhat
randomly. Am I understanding correctly?
--Larry Garfield
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