note 55648 added to language.references.pass

Don't use pass-by-reference when you want to modify large arrays. Instead, just pass by copy and return the modified array, or use the PHP functions array_map, array_walk, the latter being just a tiny bit quicker. Test script: (you may lower N to 12 or 11 on slower PC's) <?php set_time_limit(0); // it will take some time... define("N", 13); // number of arrays // calculate time in ms function microtime_float() { list($usec, $sec) = explode(" ", microtime()); return ((float)$usec + (float)$sec); } // 4 different simple array modifiers: function doSomethingByRef(& $a) { for($i = 0; $i < sizeof($a); $i++) $a[$i]++; } function doSomethingByCopy($a) { for($i = 0; $i < sizeof($a); $i++) $a[$i]++; return $a; } function doSomethingWalk($i) { $i++; } function doSomethingMap($i) { return ++$i; } // end modifiers // test function call N times and // take time sample after each test: function testFunctionCall($call) { // setup N arrays of 2^N length $b = array(); for($i = 0; $i < N; $i++) { $b[$i] = array(); for($j = 0; $j < pow(2, $i); $j++) $b[$i][$j] = 0; } // call function on N arrays $samples = array(); for($i = 0; $i < N; $i++) { $a = $b[$i]; array_push($samples, microtime_float()); eval($call); } array_push($samples, microtime_float()); return $samples; } // run tests on 4 array modifiers: $byRef = testFunctionCall("doSomethingByRef(\\$a);"); $byCpy = testFunctionCall("\\$a = doSomethingByCopy(\\$a);"); $byMap = testFunctionCall("\\$a = array_map(\\"doSomethingMap\\", \\$a);"); $byWlk = testFunctionCall("array_walk(\\$a,\\"doSomethingWalk\\");"); // output result: echo "<pre>"; echo "Size\\tPassed array by Ref\\tReturn modified array\\t"; echo "Use array_map\\t\\tUse array_walk\\n"; echo "--------------------------------------------------"; echo "--------------------------------------------------\\n"; for($i = 1; $i < sizeof($byCpy); $i++) { echo pow(2, $i - 1)."\\t"; echo str_pad($byRef[$i] - $byRef[$i-1], 20)."\\t"; echo str_pad($byCpy[$i] - $byCpy[$i-1], 20)."\\t"; echo str_pad($byMap[$i] - $byMap[$i-1], 20)."\\t"; echo str_pad($byWlk[$i] - $byWlk[$i-1], 20)."\\n"; } ?> ---- Manual Page -- http://www.php.net/manual/en/language.references.pass.php Edit -- http://master.php.net/manage/user-notes.php?action=edit+55648 Delete: added to the manual -- http://master.php.net/manage/user-notes.php?action=delete+55648&report=yes&reason=added+to+the+manual Delete: bad code -- http://master.php.net/manage/user-notes.php?action=delete+55648&report=yes&reason=bad+code Delete: spam -- http://master.php.net/manage/user-notes.php?action=delete+55648&report=yes&reason=spam Delete: useless -- http://master.php.net/manage/user-notes.php?action=delete+55648&report=yes&reason=useless Delete: non-english -- http://master.php.net/manage/user-notes.php?action=delete+55648&report=yes&reason=non-english Delete: other reasons -- http://master.php.net/manage/user-notes.php?action=delete+55648&report=yes Reject -- http://master.php.net/manage/user-notes.php?action=reject+55648&report=yes Search -- http://master.php.net/manage/user-notes.php