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Date: Wed, 4 Mar 2020 12:35:00 -0600
Message-ID: <CAESVnVrsAbAgVBg80pCgt0S_exPMSg0HF22sQ2Of6xpDksaOKQ@mail.gmail.com>
To: Nikita Popov <nikita.ppv@gmail.com>
Cc: PHP internals <internals@lists.php.net>
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Subject: Re: [PHP-DEV] Make sorting stable
From: pollita@php.net (Sara Golemon)

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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 "stabl=
e
>> 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 a=
nd
> you get Garbage-In-Garbage-Out.
>
> Roger that, thanks for explaining. =F0=9F=91=8D


> 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-eve=
n-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 fro=
m
> 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 =3D $compare($a, $b);
> if ($result !=3D=3D false) {
>     return (int) $result; // Normal behavior
> }
>
> // Bad comparison function, try the reverse order as well
> return -$compare($b, $a);
>
>
=C2=BFPor 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

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