foreach and current()

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?

current() implementation predates foreach and is totally separate. Main
difference is, that current()'s "pointer" is attached to the array, and
foreach's pointer is external.

so you can not run several each()/current() loops on array at the same
time, but you can have any number of nested foreach's iterating over the
same array independently.

They can't really be combined because of backwards compatibility

--
Alexey Zakhlestin
CTO at Grids.by/you
https://github.com/indeyets
PGP key: http://indeyets.ru/alexey.zakhlestin.pgp.asc

On Mon, Nov 18, 2013 at 3:14 PM, Nicolai Scheer scope@planetavent.dewrote:

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