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Date: Sun, 27 Dec 2009 17:01:31 +0100
Message-ID: <b54d0abe0912270801o6bb39a01x63ceecaf23701660@mail.gmail.com>
To: Mike Wacker <mwacker@cornellsun.com>
Cc: internals@lists.php.net
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Subject: Re: [PHP-DEV] Unsetting loop variables at the end of the loop
From: tyra3l@gmail.com (Ferenc Kovacs)

On Sun, Dec 27, 2009 at 3:11 PM, Mike Wacker <mwacker@cornellsun.com> wrote=
:
> Adam Harvey wrote:
>>
>> 2009/12/27 Mike Wacker <mwacker@cornellsun.com>:
>>>
>>> PHP's documentation for foreach states that if you iterate by reference
>>> [foreach ($ii as &$i) ...], you should unset $i after the loop. =C2=A0$=
i still
>>> points to the last element of the array - updating $i or reusing it wil=
l
>>> update the last element of the array.
>>>
>>> In short, why doesn't PHP automatically unset $i after the loop? =C2=A0=
I can't
>>> think of too many cases where you would want to hold on to that referen=
ce
>>> after you exit the loop, but I can think of a lot of scenarios where a
>>> user
>>> could accidentally tamper the array by using $i in a different context
>>> later
>>> on (especially since loop variable names often are reused).
>>
>> This is a bit of a FAQ, frankly. May I suggest reading this thread
>> from a couple of months ago:
>> http://marc.info/?l=3Dphp-internals&m=3D125617546815934&w=3D2. There are
>> some more discussions both on the list and in the bug tracker if you
>> want to have a bit more of a dig into this.
>
> Ah, so it seems that "reference" was the keyword I was missing in my sear=
ch
> queries for the bug database. =C2=A0It looks like I may have (re)opened a=
 can of
> worms.
>
>> The really, really short version is that it would break backward
>> compatibility to change it now,
>
> I would agree that if this did change, it would have to change in PHP 6 a=
nd
> not 5.2/3.
>
I would like to see this change in PHP6. :)
>> it's useful in some (admittedly limited) cases,
>
> The main problem I see is that, like you said, these cases are limited. =
=C2=A0If
> you really need to hold on to a reference after the loop, then why not ma=
ke
> an explicit reference?
>
> foreach ($ii as &$i) {
> =C2=A0$j =3D$ $i;
> =C2=A0// loop body
> } // PHP implicitly unset()'s $i
>
> In both this case and the status quo, someone has to add an extra line of
> code for every loop. =C2=A0Since re-using a loop variable is a much more =
common
> use case, I feel that PHP should accommodate that use case and force peop=
le
> using references outside the loop to add the line of code instead.
>
>> and it's not as though it's not well documented as behaving that way.
>>
>> Adam
>
> True, but it may not hurt to make the documentation more explicit to catc=
h
> the most common use case. =C2=A0You could add this clause: ", especially =
if
> $value is used elsewhere as a loop variable again." (Though should I mayb=
e
> move this part into the doc newsgroup?)
>
>
>
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