bug when using foreach with references? View as Markdown

I don't follow. Is this really the intended behavior? It seems quite
unintuitive that the original array would be modified by empty
loops.

It is intended behaviour. Consider your code; at the end of this loop:

$items = array('apple', 'banana', 'carrot');
print_r($items);
foreach ($items as &$item) { }

$item will contain a reference to the last item of $items. Therefore,
when you start the next loop:

foreach ($items as $item) { }

$item will receive each of the values stored in $items, in sequence.
But $item is a reference to the last item in $items, so whatever you
write into it will also be written into the last item of the array.
Thus, the loop will cause these values to be written there:

• On the first iteration, "apple"
• On the second iteration, "banana"
• On the third iteration, "banana" (because you are taking the third
  item in the array, which you just overwrote)

When would this behavior be desired?

Probably never, but that does not make it counterintuitive—the
interpreter is behaving correctly based on the data it is handling and
the instructions you are giving to it. The correct solution, as
someone has already recommended, is to unset the iterator if you want
to reuse it.

Cheers,

Marco.

Richard K Miller wrote:

It is one of these things that make perfect sense when you think about
it a little bit. Yes, it catches some people, just like strpos()
returning character position 0 on a first-char match catches some
people. There is no way to fix things like these without completely
breaking things. If we had strpos not use 0-based string positions or
if we arbitrarily broke references after loops, all sorts of other
things would start breaking and no longer make sense.

-Rasmus

Rasmus,

Thanks for your reply. With respect, this seems to be in a different
class from matching strings with character position 0, IMO.

What about unsetting the iterator before foreach() looping begins? The
iterator is altered anyway, so would this prevent it from being
"attached" to previous foreach() iterations?

It would be arbitrarily breaking an explicit reference. I know I have
code lying around that relies on multiple loops cleaning up a big
complicated multi-level array. I do ugly things with references into
that array and it would completely break if PHP magically deleted my
references whether they are in the iterator or elsewhere.

This has been this way for 6+ years and it is well documented on the
http://php.net/foreach page. (see the big red warning box)

-Rasmus