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<?php $a = array(23 => 'a1', 108 => 'a2', 45 => 'a3'); $b = array(18 => 'b1', 30 => 'b2', 100 => 'b3'); var_dump(array_merge($a, $b)); var_dump(array_merge($b, $a));
Output for 4.3.0 - 5.6.28, hhvm-3.10.0 - 3.12.0, 7.0.0 - 7.1.0
array(6) { [0]=> string(2) "a1" [1]=> string(2) "a2" [2]=> string(2) "a3" [3]=> string(2) "b1" [4]=> string(2) "b2" [5]=> string(2) "b3" } array(6) { [0]=> string(2) "b1" [1]=> string(2) "b2" [2]=> string(2) "b3" [3]=> string(2) "a1" [4]=> string(2) "a2" [5]=> string(2) "a3" }