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<?php $a = array( '0' => 'null' ); $b = array( 0 => 'zero' ); var_dump($a); var_dump($b); var_dump(array_merge($a, $b)); var_dump(array_merge($b, $a)); var_dump($a + $b);
Output for 4.3.0 - 5.6.28, hhvm-3.10.0 - 3.12.0, 7.0.0 - 7.1.0
array(1) { [0]=> string(4) "null" } array(1) { [0]=> string(4) "zero" } array(2) { [0]=> string(4) "null" [1]=> string(4) "zero" } array(2) { [0]=> string(4) "zero" [1]=> string(4) "null" } array(1) { [0]=> string(4) "null" }