run code in 200+ php & hhvm versions
Bugs & Features
<?php $z1 = "abc"; $out = ""; for ($i = 0; $i < strlen($z1); $i++) { $out[$i] = $z1[$i]; // $out = $out.$z1[$i]; } print_r $out;

Here you find the average performance (time & memory) of each version. A grayed out version indicates it didn't complete successfully (based on exit-code).
Note: hhvm uses a JIT which only kicks in after a few runs. Since we run scripts only once, hhvm always runs slower.

VersionSystem time (s)User time (s)Memory (MiB)