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<?php $a = array('1'=>'a1','2'=>'a2','a'=>'1'); $b = array('2'=>'b2','b'=>'2'); var_dump($a+$b); var_dump($b+$a); var_dump(array_merge($a,$b)); var_dump(array_merge($b,$a));
Output for 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 - 8.1.27, 8.2.0 - 8.2.17, 8.3.0 - 8.3.4
array(4) { [1]=> string(2) "a1" [2]=> string(2) "a2" ["a"]=> string(1) "1" ["b"]=> string(1) "2" } array(4) { [2]=> string(2) "b2" ["b"]=> string(1) "2" [1]=> string(2) "a1" ["a"]=> string(1) "1" } array(5) { [0]=> string(2) "a1" [1]=> string(2) "a2" ["a"]=> string(1) "1" [2]=> string(2) "b2" ["b"]=> string(1) "2" } array(5) { [0]=> string(2) "b2" ["b"]=> string(1) "2" [1]=> string(2) "a1" [2]=> string(2) "a2" ["a"]=> string(1) "1" }

preferences:
152.73 ms | 404 KiB | 152 Q