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run code in 150+ php & hhvm versions
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<?php $days = array('2'); function alter_days(&$day) { $day = 'bla'; } array_filter($days, 'alter_days'); var_dump($days);
Output for hhvm-3.10.0 - 3.12.0, 7.0.0 - 7.1.0
array(1) { [0]=> string(1) "2" }
Output for 4.3.0 - 5.6.28
array(1) { [0]=> string(3) "bla" }