Why is calling a function (such as strlen, count etc) on a referenced value so slow?

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I found a bug report from 2005 that describes exactly this issue: http://bugs.php.net/bug.php?id=34540

So the problem seems to be that when passing a referenced value to a function that doesn’t accept a reference, PHP needs to copy it.

This can be demonstrated with this test code:

<?php
function CalledFunc(&$aData)
{
    // Do nothing
}

function TestFunc(&$aArray)
{
    $aArray = range(0, 100000);
    $fStartTime = microtime(true);

    for ($iIter = 0; $iIter < 1000; $iIter++)
    {
        CalledFunc($aArray);
    }

    $fTaken = microtime(true) - $fStartTime;

    print "took $fTaken seconds\n";
}

$aArray = array();
TestFunc($sData);
?>

This runs quickly, but if you change function CalledFunc(&$aData) to function CalledFunc($aData) you’ll see a similar slow-down to the count example.

This is rather worrying, since I’ve been coding PHP for quite a while and I had no idea about this issue.

Fortunately there’s a simple workaround that is applicable in many cases – use a temporary local variable inside the loop, and copy to the reference variable at the end.

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