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To: Nikita Popov <nikita.ppv@gmail.com>
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Date: Thu, 5 Mar 2020 15:11:11 +0100
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Subject: Re: [PHP-DEV] Make sorting stable
From: cmbecker69@gmx.de ("Christoph M. Becker")

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#L37=
2>
>
> 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 i=
n
> extension code) always returns "greater-than" for non-equal elements. Th=
e
> end result here is that the sort will not have any defined order regardl=
ess
> 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 m=
ay
> want to make the "not ordered" case more explicit, in which case we coul=
d
> throw a warning when such comparisons are performed as part of sorting.

ACK.

=2D-
Christoph M. Becker