`isset` is twice faster than `strlen`

strlen_isset_test.php

<?php

$strs = [];
$s = str_repeat("0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ", 10);
$n = 100000;

for ($i = 0; $i < $n; $i++) {
    $strs[$i] = substr(str_shuffle($s), 0, mt_rand(10, 100));
}

$t1 = $t2 = 0;

$start = microtime(1);
$c1 = 0;
for ($i = 0; $i < $n; $i++) {
    if (strlen($strs[$i]) > 60) {
        $c1++;
    }
}
$t1 = microtime(1) - $start;

$start = microtime(1);
$c2 = 0;
for ($i = 0; $i < $n; $i++) {
    if (isset($strs[$i][60])) {
        $c2++;
    }
}
$t2 = microtime(1) - $start;

echo "isset:  {$t2} ({$c2})\nstrlen: {$t1} ({$c1})\n";

// 3 runs:
// ------
// isset:  0.060104131698608 (44030)
// strlen: 0.13449788093567 (44030)
//
// isset:  0.058434963226318 (44055)
// strlen: 0.13221907615662 (44055)
// 
// isset:  0.060664176940918 (43928)
// strlen: 0.14264702796936 (43928)

Based on http://blog.blackfire.io/owncloud.html