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<?php $days = array('2'); function alter_days(&$day) { return $day -= 1; } array_filter($days, 'alter_days'); var_dump($days);
Output for 8.0.0 - 8.0.30, 8.1.0 - 8.1.28, 8.2.0 - 8.2.18, 8.3.0 - 8.3.6
Warning: alter_days(): Argument #1 ($day) must be passed by reference, value given in /in/C5EVo on line 11 array(1) { [0]=> string(1) "2" }
Output for 7.0.0 - 7.0.33, 7.1.0 - 7.1.33, 7.2.0 - 7.2.33, 7.3.0 - 7.3.33, 7.4.0 - 7.4.33
array(1) { [0]=> string(1) "2" }
Output for 4.3.0 - 4.3.11, 4.4.0 - 4.4.9, 5.0.0 - 5.0.5, 5.1.0 - 5.1.6, 5.2.0 - 5.2.17, 5.3.0 - 5.3.29, 5.4.0 - 5.4.45, 5.5.0 - 5.5.38, 5.6.0 - 5.6.40
array(1) { [0]=> int(1) }

preferences:
317.29 ms | 403 KiB | 460 Q