note 55152 added to control-structures.foreach

Using PHP5's foreach "as reference" can bite you! Three guys in my office spent about a day chasing this one's tail, that was causing aberrant behavior in the values of elements of an array. It turns out to be a consequence of the nature of references, generally. If you create a reference to a variable, all names for that variable (including the original) BECOME REFERENCES. To paraphrase "The Highlander," if you want a name to OWN a piece of data, "there can be only one." To illustrate this point, consider the following code: <?php $f = array( 0 => array('value' => 'three'), 1 => array('value' => 'three') ); foreach ( $f as $k => &$v ) { $v['value'] = 'one'; } $a = $f; $b = $f; $b[0]['value'] = 'two'; $b[1]['value'] = 'two'; var_dump($a, $b); ?> Upon execution, you will find that, although you would expect $a to contain two arrays with 'value' of 'one', $a and $b are identical -- i.e., the changes of []['value'] to 'two' have happened in both arrays. But, upon further examination of the var_dumps, you will see that both sets' elements [0] and [1] are preceded with "&": they are references! The easy solution to this problem turns out to be: unset the foreach "as-reference" variable ($v) at the bottom of your foreach loop. This allows the original variable (or array member) to resume ownership of the value and dissolves its "reference-ness". ---- Manual Page -- http://www.php.net/manual/en/control-structures.foreach.php Edit -- http://master.php.net/manage/user-notes.php?action=edit+55152 Delete: added to the manual -- http://master.php.net/manage/user-notes.php?action=delete+55152&report=yes&reason=added+to+the+manual Delete: bad code -- http://master.php.net/manage/user-notes.php?action=delete+55152&report=yes&reason=bad+code Delete: spam -- http://master.php.net/manage/user-notes.php?action=delete+55152&report=yes&reason=spam Delete: useless -- http://master.php.net/manage/user-notes.php?action=delete+55152&report=yes&reason=useless Delete: non-english -- http://master.php.net/manage/user-notes.php?action=delete+55152&report=yes&reason=non-english Delete: other reasons -- http://master.php.net/manage/user-notes.php?action=delete+55152&report=yes Reject -- http://master.php.net/manage/user-notes.php?action=reject+55152&report=yes Search -- http://master.php.net/manage/user-notes.php