php-general Digest 26 Mar 2012 06:39:23 -0000 Issue 7745
Topics (messages 317260 through 317262):
Re: foreach weirdness
317260 by: Matijn Woudt
317261 by: Simon Schick
317262 by: Arno Kuhl
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--- Begin Message ---
On Sun, Mar 25, 2012 at 4:11 PM, Arno Kuhl <a...@dotcontent.net> wrote:
> From: Simon Schick [mailto:simonsimc...@googlemail.com]
> Sent: 24 March 2012 12:30 AM
> To: Robert Cummings
> Cc: a...@dotcontent.net; php-gene...@lists.php.net
> Subject: Re: [PHP] foreach weirdness
>
> 2012/3/23 Robert Cummings <rob...@interjinn.com>
>>
>> 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@lists.php.net/msg269552.html
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--- Begin Message ---
2012/3/25 Arno Kuhl <a...@dotcontent.net>:
>
> 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.
>
Hi, Arno
Requesting that will at least require a major-release (f.e. PHP 6.0)
... but I would rather request to add a notice or warning to the
documentation of references to remind stuff like that.
http://www.php.net/manual/en/language.references.php
I think this is stuff more people will stumble over ...
Bye
Simon
--- End Message ---
--- Begin Message ---
Requesting that will at least require a major-release (f.e. PHP 6.0) ... but I
would rather request to add a notice or warning to the documentation of
references to remind stuff like that.
http://www.php.net/manual/en/language.references.php
I think this is stuff more people will stumble over ...
Bye
Simon
--
I agree it would be wrong to change php's handling of call by reference in
foreach loops because there may be a need to access that reference after
completing the loop. I was going to suggest there should be a warning in the
manual to unset the reference after the foreach loop is completed, but I see
the current online manual has that warning prominently displayed on the foreach
page. I had a version of the manual from July last year that didn't have the
warning, so I'll update my local manual and make sure I keep it up to date.
Lesson learned (both manual and foreach references).
Cheers
Arno
--- End Message ---
