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Date: Sat, 29 Jun 2019 20:04:18 +0200
Message-ID: <CANZOY=BHf1y0PWmQ5qOKqoz8wbfFOT7-D5LnvcXpiRaDPiv0LA@mail.gmail.com>
To: Rowan Collins <rowan.collins@gmail.com>
Cc: PHP Internals <internals@lists.php.net>
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Subject: Re: [PHP-DEV][RFC] Normalize array's "auto-increment" value on copy
 on write
From: arnold.adaniels.nl@gmail.com (Arnold Daniels)

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On Thu, 20 Jun 2019, 19:06 Rowan Collins, <rowan.collins@gmail.com> wrote:

> On Thu, 20 Jun 2019 at 13:11, Wes <netmo.php@gmail.com> wrote:
>
> > I left that out of scope for the RFC, for reasons I don't have the
> > knowledge to describe properly. In the following example, `unset()`
> should
> > reset the auto increment to `1` only after the third `unset()` call
> >
> > ```
> > $array = [0, 1, 2, 3]; // auto increment is 4 because there are "holes"
> in
> > the index
> > unset($array[1]); // auto increment is still 4
> > unset($array[2]); // auto increment is still 4
> > unset($array[3]); // auto increment is 1, because the index sequence is
> > contiguous, without holes
> > ```
> >
>
>
> I wonder if it would be possible (and sufficient) to detect if the element
> being removed was the highest key, and only then look for the new "next"
> value.
>
> The new value can be found either by decrementing the known value until you
> hit an existing entry (optimal for large arrays with few gaps in the
> sequence of keys) or by checking all the keys and finding the max (optimal
> for small but sparse arrays like [12, 145, 65546]).
>
> # pseudocode:
>
> if ( key_being_unset == array.next_key - 1 ) {
>     if ( short_or_likely_to_be_sparse(array) ) {
>         new_highest_key = max(array.keys);
>     } else {
>         # Find highest unused number, starting from the one just deleted
>         do {
>             new_highest_key = key_being_unset - 1;
>         } while ( not key_exists(array, new_highest_key) );
>         array.next_key = new_highest_key + 1;
>     }
> }
>
>
> I've no idea if this is plausible or not.
>
> Regards,
> --
> Rowan Collins
> [IMSoP]
>

As you state; this change is not BC. I'm not sure if I agree that this
should be considered a simple bugfix.

Maybe it would be good to add a secondary vote to decide if this should be
implemented in PHP 7.4 or PHP 8.

Arnold

>

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