Bug #29992 [Com]: foreach by reference corrupts the array

Edit report at https://bugs.php.net/bug.php?id=29992&edit=1 ID: 29992 Comment by: xjis at msn dot com Reported by: fletch at pobox dot com Summary: foreach by reference corrupts the array Status: Not a bug Type: Bug Package: Scripting Engine problem Operating System: linux PHP Version: 5.0.1 Block user comment: N Private report: N New Comment: guys... i read through this entire thread and now i totally get it. this is just a weird "side-effect" of having a language being "function-level scope" instead of "block-level scope" and with referencing support. and as long as the language stays being 'function-level scope' that also has the referencing support, this is the expected behavior; and there's no easy way around it. what ppl are expecting is exactly that of a block-level scope languages: having &v not referencing anything after for-loop block ended. that's why ppl are keep referring to C/C++/Java because these are all block-level scope languages; and why everyone wants for-loop to "auto-unset" the &v after for-loop block ended; that would basically emulate/mimic the behavior of block-level scope languages; but that is simply not the expected behavior for function-level scope languages so you can't just make a special case only for for-loop blocks --why would you make a special exception just for for-loop; why not for the entire language? then now, you are asking PHP language to completely change itself from being a function-level scope language into a block-level scope language btw, javascript is also a function-level scope language, but it doesn't have this particular problem because it doesn't support referencing Previous Comments: ------------------------------------------------------------------------ [2013-12-04 21:50:33] gray dot bowman at gmail dot com Just wanted to chime in that 9 years on, this is still totally unexpected behavior. Today, two professional developers with years experience spent a couple hours trying to figure out why an array that was demonstrably intact had its last element corrupted for apparently no reason once entering a foreach. ------------------------------------------------------------------------ [2013-05-21 06:38:43] email at stevemann dot net Agreed this is not a bug, it's expected behaviour. But it's dangerous as it can slip by without being noticed. It almost certainly means there are thousands of sites which are exhibiting wrong behaviour because of this and no-one realises. Surely the concept of scoping the 'as' variable to the foreach enclosure only can't be considered bad form. It would make so much more sense to 'opt-in' to retrieving the variable outside of the enclosure (by assigning to another persistent variable within the enclosure) rather than the current 'opt-out' system (using unset()) which, unless you happen to have read the warning is HIGHLY DANGEROUS. ------------------------------------------------------------------------ [2013-05-20 15:57:18] paul dot dillinger at gmail dot com OK, I went over this some more. <pre> <?php // Fresh array $clean = array(1,2,3,4); foreach($clean as &$item){ // Nothing is modified in the array, but $item now exists } /*############################################################################## * $item persists outside of foreach and is now $clean[3] * See the warning on http://php.net/manual/en/control-structures.foreach.php * print_r($item); // would return 4 you you uncommented this. * unset($item); // This would remove the pointer to $clean[3]. Expected. *############################################################################*/ echo "A:\n"; /*A*/ print_r($clean); // $clean is still unmodified echo "B:\n"; foreach($clean as $item){ /*############################################################################## * Using AS $item SETS $item TO the current $item value (a.k.a. $clean[0], etc.) * Essentially foreach($clean as $item) is short hand for something like: * $x=0;while($x < count($clean)){$item=$clean[$x]; ### your code ### $x++;} * The problem I had was that I did not expect foreach to be able to set on call *############################################################################*/ /*B*/ print_r($clean); } ?> </pre> So creating the variable is documented, and it isn't a bug. The ability to set the value could be made clearer though. ------------------------------------------------------------------------ [2013-05-20 09:51:33] richard at ejem dot cz This IS a bug and SHOULD be finally fixed. It is weird, hard to debug and unexpected behavior which took me many hours of life finding the problem. Almost every modern programming language has a variable context, which guarrantees the foreach variable is not visible after exiting the loop. Anyone is using it intentionally for "weird reason"? come on guys, almost every bug can be used for some hacking or weird reasons, will it stop you from fixing other bugs? no! Sorry for "mee-to" like post, but I do it for the good of next PHP programmer generations who will also lose hours of their lives discovering this nonsense. Please fix it. ------------------------------------------------------------------------ [2012-10-25 17:01:03] paul dot dillinger at gmail dot com I understand that my explanation above isn't 100% accurate (unset really doesn't have anything to do with it), but that doesn't change that the expected behavior is not working. Rasmus said: "Ok, simple question then. Do you expect this to output 3? foreach(array(1,2,3) as $b) { } echo $b; If you do, then you don't want us to fix this "bug" because fixing it would mean $b is not 3 here." I say in the example above, would you expect a print_r of the same array to return 1,2,2? My issue was that the content of the entire array. Honestly I've been programming since I was eight years old. That was 1985. If this was confusing the hell out of me then something's wrong. Here's an even simpler example: <pre> <?php $clean = array(1,2,3,4); foreach($clean as &$item){ // Nothing } echo "A:\n"; /*A*/ print_r($clean); echo "B:\n"; foreach($clean as $item){ /*B*/ print_r($clean); } $clean = array(1,2,3,4); foreach($clean as &$item){ // Nothing } echo "C:\n"; /*C*/ print_r($clean); echo "D:\n"; foreach($clean as $not_item){ /*C*/ print_r($clean); } ?> </pre> A and B output the same array differently with no modification (not expected). C and D are the same (expected). The only change was not re-using the name $item. How can we make it so that using &$item in one foreach and then using the same variable name ($item) in a different foreach does not change the original array? ------------------------------------------------------------------------ The remainder of the comments for this report are too long. To view the rest of the comments, please view the bug report online at https://bugs.php.net/bug.php?id=29992 -- Edit this bug report at https://bugs.php.net/bug.php?id=29992&edit=1