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<?php $dates = [null, '2015-12-30', new \DateTime('now')]; foreach ($dates as &$date) { if ($date instanceof \DateTime) { $date = $date->format('Y-m-d'); } } var_dump($dates);
Output for 5.6.28, 7.0.20, 7.1.0 - 7.1.20, 7.2.0 - 7.2.33, 7.3.16 - 7.3.33, 7.4.0 - 7.4.33, 8.0.0 - 8.0.30, 8.1.0 - 8.1.28, 8.2.0 - 8.2.19, 8.3.0 - 8.3.7
array(3) { [0]=> NULL [1]=> string(10) "2015-12-30" [2]=> &string(10) "2015-12-30" }
Output for 7.0.6
array(3) { [0]=> NULL [1]=> string(10) "2015-12-30" [2]=> &string(10) "2016-05-21" }
Output for 7.0.5
array(3) { [0]=> NULL [1]=> string(10) "2015-12-30" [2]=> &string(10) "2016-04-03" }
Output for 7.0.4
array(3) { [0]=> NULL [1]=> string(10) "2015-12-30" [2]=> &string(10) "2016-03-10" }
Output for 7.0.3
array(3) { [0]=> NULL [1]=> string(10) "2015-12-30" [2]=> &string(10) "2016-03-18" }
Output for 7.0.2
array(3) { [0]=> NULL [1]=> string(10) "2015-12-30" [2]=> &string(10) "2016-03-23" }
Output for 7.0.1
array(3) { [0]=> NULL [1]=> string(10) "2015-12-30" [2]=> &string(10) "2016-03-24" }
Output for 7.0.0
array(3) { [0]=> NULL [1]=> string(10) "2015-12-30" [2]=> &string(10) "2016-03-27" }
Output for 5.6.21
array(3) { [0]=> NULL [1]=> string(10) "2015-12-30" [2]=> &string(10) "2016-05-02" }
Output for 5.6.20
array(3) { [0]=> NULL [1]=> string(10) "2015-12-30" [2]=> &string(10) "2016-04-10" }
Output for 5.6.19
array(3) { [0]=> NULL [1]=> string(10) "2015-12-30" [2]=> &string(10) "2016-03-08" }
Output for 5.6.18
array(3) { [0]=> NULL [1]=> string(10) "2015-12-30" [2]=> &string(10) "2016-03-15" }
Output for 5.6.17
array(3) { [0]=> NULL [1]=> string(10) "2015-12-30" [2]=> &string(10) "2016-03-20" }
Output for 5.6.16
array(3) { [0]=> NULL [1]=> string(10) "2015-12-30" [2]=> &string(10) "2016-03-28" }
Output for 5.6.15
array(3) { [0]=> NULL [1]=> string(10) "2015-12-30" [2]=> &string(10) "2016-03-29" }
Output for 5.6.14
array(3) { [0]=> NULL [1]=> string(10) "2015-12-30" [2]=> &string(10) "2016-04-14" }
Output for 5.6.13
array(3) { [0]=> NULL [1]=> string(10) "2015-12-30" [2]=> &string(10) "2016-04-15" }
Output for 5.6.12
array(3) { [0]=> NULL [1]=> string(10) "2015-12-30" [2]=> &string(10) "2016-04-20" }
Output for 5.6.11
array(3) { [0]=> NULL [1]=> string(10) "2015-12-30" [2]=> &string(10) "2016-04-24" }
Output for 5.6.10
array(3) { [0]=> NULL [1]=> string(10) "2015-12-30" [2]=> &string(10) "2016-04-25" }
Output for 5.6.9
array(3) { [0]=> NULL [1]=> string(10) "2015-12-30" [2]=> &string(10) "2016-04-27" }
Output for 5.6.8
array(3) { [0]=> NULL [1]=> string(10) "2015-12-30" [2]=> &string(10) "2016-04-30" }
Output for 5.5.35
array(3) { [0]=> NULL [1]=> string(10) "2015-12-30" [2]=> &string(10) "2016-05-23" }
Output for 5.5.34
array(3) { [0]=> NULL [1]=> string(10) "2015-12-30" [2]=> &string(10) "2016-04-11" }
Output for 5.5.33
array(3) { [0]=> NULL [1]=> string(10) "2015-12-30" [2]=> &string(10) "2016-03-09" }
Output for 5.5.32
array(3) { [0]=> NULL [1]=> string(10) "2015-12-30" [2]=> &string(10) "2016-03-17" }
Output for 5.5.31
array(3) { [0]=> NULL [1]=> string(10) "2015-12-30" [2]=> &string(10) "2016-03-21" }
Output for 5.5.30
array(3) { [0]=> NULL [1]=> string(10) "2015-12-30" [2]=> &string(10) "2016-04-01" }
Output for 5.5.29
array(3) { [0]=> NULL [1]=> string(10) "2015-12-30" [2]=> &string(10) "2016-04-17" }
Output for 5.5.28
array(3) { [0]=> NULL [1]=> string(10) "2015-12-30" [2]=> &string(10) "2016-04-21" }
Output for 5.5.27
array(3) { [0]=> NULL [1]=> string(10) "2015-12-30" [2]=> &string(10) "2016-04-22" }
Output for 5.5.26
array(3) { [0]=> NULL [1]=> string(10) "2015-12-30" [2]=> &string(10) "2016-04-26" }
Output for 5.5.25
array(3) { [0]=> NULL [1]=> string(10) "2015-12-30" [2]=> &string(10) "2016-04-29" }
Output for 5.5.24
array(3) { [0]=> NULL [1]=> string(10) "2015-12-30" [2]=> &string(10) "2016-05-24" }

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