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Date: Mon, 18 Nov 2013 17:02:18 +0100
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To: Nicolai Scheer <scope@planetavent.de>
Cc: PHP internals <internals@lists.php.net>
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Subject: Re: [PHP-DEV] foreach and current()
From: nikita.ppv@gmail.com (Nikita Popov)

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On Mon, Nov 18, 2013 at 3:14 PM, Nicolai Scheer <scope@planetavent.de>wrote:

> Hi all!
>
> Has it been always the way, that it is not possible to use current() in a
> foreach loop?
>
> Just stumbled upon (using php 5.5.5):
>
> $arr = array( "a", "b", "c" );
>
> foreach( $arr as $entry )
> {
>     #var_dump( current($arr) );
> }
>
> var_dump( current($arr) );
>
> Which yields "false", because the internal array pointer points behind the
> last element of $arr.
> If I uncomment the inner var_dump(), the script outputs "b" four times.
> This seems odd... I know that the documentation advises not to fiddle with
> the internal array pointer in a foreach loop, but current() should not
> affect it in any way and therefor should be safe to use.
>
> Does anyone know what the reasoning behind this behavious is?
>

The relation between foreach and current() is somewhat complex and depends
on the environment, in particular the refcount of the array, whether it is
a reference and whether the iteration happens by-reference. The exact
behavior and the reasons for it are outlined in
http://stackoverflow.com/questions/10057671/how-foreach-actually-works/14854568#14854568
.

I have a patch attached to bug #53405 (https://bugs.php.net/bug.php?id=53405)
to make foreach and current() fully independent (and provide generally
stronger independence and safety guarantees in that area), but it's a
somewhat tricky affair and I likely won't have time to finish this for 5.6.

Nikita

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