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To: Sara Golemon <pollita@php.net>, "Christoph M. Becker" <cmbecker69@gmx.de>
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Date: Wed, 17 May 2017 00:21:31 +0200
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Subject: Re: [PHP-DEV] BC break in master (7.2) - Distinguish
 betweenunmatchedsubpatterns and empty matches in preg_*()
From: cmbecker69@gmx.de ("Christoph M. Becker")

On 17.05.2017 at 00:13, Sara Golemon wrote:

> 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.

Personally, I rarely use array_key_exists(), but others may prefer it,
and it appears to be cleaner not to set unmatched subpatterns at all.
And if we're going to add a flag anyway, it appears to be reasonable to
change the behavior right away, i.e. to introduce something like
PREG_SKIP_UNMATCHED instead of PREG_UNMATCHED_AS_NULL.

-- 
Christoph M. Becker