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Date: Tue, 16 May 2017 17:13:42 -0500
Message-ID: <CAESVnVoRu1swOonzksv+TWu+7sJ0eb3H9pKroYOEP17hxHooqA@mail.gmail.com>
To: "Christoph M. Becker" <cmbecker69@gmx.de>
Cc: Remi Collet <remi@fedoraproject.org>, PHP internals <internals@lists.php.net>
Content-Type: text/plain; charset="UTF-8"
Subject: Re: [PHP-DEV] BC break in master (7.2) - Distinguish betweenunmatched
 subpatterns and empty matches in preg_*()
From: pollita@php.net (Sara Golemon)

On Tue, May 16, 2017 at 5:03 PM, Christoph M. Becker <cmbecker69@gmx.de> wrote:
>>> I suggest not to set unmatched subpatterns at all,
>>
>> Can you give an example of expected output ?
>> (I think stable position for matched pattern is important)
>>
>> php -r 'var_dump(preg_match("/(a)?([a-z]*)(\d*)/", "123", $matches),
>> $matches);'
>
> See the pcretest results danielklein posted in his last comment on
> <https://bugs.php.net/61780>.  Basically, instead of assigning NULL as
> values, the array indexes could be skipped, so that array_key_exists()
> can be used to determine whether a certain subpattern matched or not.
>
Well, but isset() would do this already with NULLs.

$x = ['foo'=>NULL];
// isset($x['foo'] === false)

I know people are generally getting trained to use array_key_exists()
to avoid this "set but null" issue, but this is a case where that
behavior of isset() is actually quite useful.

-Sara