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Date: Sat, 17 Jan 2015 06:15:30 +0900
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To: Rowan Collins <rowan.collins@gmail.com>
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Subject: Re: [PHP-DEV] Fixing strange foreach behavior.
From: yohgaki@ohgaki.net (Yasuo Ohgaki)

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Hi Rowan,

On Sat, Jan 17, 2015 at 1:22 AM, Rowan Collins <rowan.collins@gmail.com>
wrote:

> Yasuo Ohgaki wrote on 16/01/2015 08:40:
>
>> Hi all,
>>
>> Take a look at
>>
>> http://3v4l.org/HbVnd
>>
>> foreach should not affect internal(zval) array position, but it does.
>> I'm not sure why foreach works this way, but HHVM behavior is
>> reasonable. IMHO.
>>
>> PHP 7 would be perfect opportunity fix this behavior.
>> Any comments?
>>
>
> I seem to remember somebody mentioning that the pointer is reused in some
> situations and not others. I think the reason is efficiency - we have a
> pointer associated with each array, which is rarely used, so why not borrow
> it for foreach? (Answer: because it causes the oddity you just spotted. :P)
>

Right. foreach should not affect internal(zval) position pointer, but it
does.


>
> For instance, if you put a reset() in the middle of the foreach loop, it
> doesn't interrupt the progress of the loop, but does cause it to be tracked
> separately and output "Apple" after the loop finishes:
> http://3v4l.org/KTCrI
>
> There are other weird cases, like nesting two foreach loops over the same
> variable:
> - with a true array, the loops are independent (both loops see the full
> set of values): http://3v4l.org/lJTQG
> - with a rewindable Traversable, such as SimpleXMLElement, they interact
> (the inner loop sees all values, but the outer loop doesn't continue after
> the inner one completes): http://3v4l.org/fs2Jv
> - with a non-rewindable Traversable, such as a Generator, PHP tries to
> rewind and gives a fatal error, while HHVM simply uses up the last values
> of the generator on the inner loop (possibly a bug?):
> http://3v4l.org/BYOmQ
>
> My conclusion: don't try and nest foreach or any related constructs using
> the same variable, because the behaviour is not guaranteed to be in any way
> sane.
>

Nesting foreach is strange, too. There are two issues
 - array nesting does not work as it seems
 - generator nesting does not work at all

Besides generator, current behavior is strange.
It's matter of using external position pointer for arrays, isn't it?

How about make foreach behaves sane manner by PHP 7?
It's rare that program uses internal position pointer, but
it's a basic language construct. Basic language construct
should behave intuitive way. IMHO.

Regards,

--
Yasuo Ohgaki
yohgaki@ohgaki.net

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