Re: foreach weirdness

[Matijn Woudt <tijnema@xxxxxxxxx>]

On Sun, Mar 25, 2012 at 4:11 PM, Arno Kuhl <arno@xxxxxxxxxxxxxx> wrote:
> From: Simon Schick [mailto:simonsimcity@xxxxxxxxxxxxxx]
> Sent: 24 March 2012 12:30 AM
> To: Robert Cummings
> Cc: arno@xxxxxxxxxxxxxx; php-general@xxxxxxxxxxxxx
> Subject: Re:  foreach weirdness
>
> 2012/3/23 Robert Cummings <robert@xxxxxxxxxxxxx>
>>
>> On 12-03-23 11:16 AM, Arno Kuhl wrote:
>>>
>>>
>>> it still does not produce the correct result:
>>> 0 1 3 6 10 15 21
>>> 0 1 3 6 10 15 15
>>
>>
>> This looks like a bug... the last row should be the same. What version
>> of PHP are you using? Have you checked the online bug reports?
>>
>>
>
> Hi, Robert
>
> Does not seem like a bug to me ...
> http://schlueters.de/blog/archives/141-References-and-foreach.html
>
> What you should do to get the expected result:
> Unset the variable after you don't need this reference any longer.
>
> Bye
> Simon
>
> --
>
> Hi Simon, unsetting the $value does fix the problem, but I found that any time you assign $value by reference in a foreach loop you have to do an unset to avoid corrupting the array unless you continue to assign $value by reference (as illustrated in the article you linked).
>
> So doing something as simple as:
> $array = array(0, 1, 2, 3, 4, 5, 6);
> foreach ($array as $key=>&$value) {
>        echo "Key: $key; Value: $value<br />\n";
> }
>
> and then follow with (from the php manual):
> foreach ($array as $key=>$value) {
>        echo "Key: $key; Value: $value<br />\n";
> }
>
> will not only give the wrong result, it will corrupt the array for *any* further use of that array. I still think it’s a bug according to the definition of foreach in the php manual. Maybe php needs to do an implicit unset at the closing brace of the foreach where was an assign $value by reference, to remove the reference to the last element (or whatever element it was pointing to if there was a break) so that it doesn't corrupt the array, because any assign to $value after the foreach loop is completed will corrupt the array (confirmed by testing). The average user (like me) wouldn't think twice about reusing $value after ending the foreach loop, not realising that without an unset the array will be corrupted.
>
> BTW thanks for that reference, it was quite an eye-opener on the pitfalls of using assign by reference, not only in the foreach loop.
>
> Cheers
> Arno

Note that somewhat similar error was discussed on this list a few
months ago[1]. You could probably have solved it yourself if you
searched the mailing list archives.

- Matijn

[1] http://www.mail-archive.com/php-general@xxxxxxxxxxxxx/msg269552.html

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