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<?php $a = array( 1 => array( 'test' => 3 ) ); $b = array( 1 => array( 'test2' => 3 ) ); $c = array_merge_recursive( $a, $b ); var_dump( $c );
Output for 5.5.0 - 5.5.35, 5.6.0 - 5.6.28, 7.0.0 - 7.0.20, 7.1.0 - 7.1.33, 7.2.6 - 7.2.33, 7.3.0 - 7.3.33, 7.4.0 - 7.4.33, 8.0.0 - 8.0.30, 8.1.0 - 8.1.27, 8.2.0 - 8.2.16, 8.3.0 - 8.3.3
array(2) { [0]=> array(1) { ["test"]=> int(3) } [1]=> array(1) { ["test2"]=> int(3) } }

preferences:
141.63 ms | 405 KiB | 236 Q