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<?php class A { var $field = array(1); } $a = new A; $x = array("a" => $a); $y = array("a" => array("field" => array(2))); var_dump(array_merge_recursive($x,$y));
Output for 5.3.0 - 5.3.29, 5.4.0 - 5.4.45, 5.5.0 - 5.5.38, 5.6.0 - 5.6.40, 7.0.0 - 7.0.33, 7.1.0 - 7.1.33, 7.2.0 - 7.2.34, 7.3.0 - 7.3.32, 7.4.0 - 7.4.25, 8.0.0 - 8.0.12, 8.1rc1 - rc3
array(1) { ["a"]=> array(1) { ["field"]=> array(2) { [0]=> int(1) [1]=> int(2) } } }

preferences:
64.54 ms | 462 KiB | 5 Q