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<?php var_dump(array_merge(["a" => 123, 555], ["a" => 666]));
Output for 5.6.38, 7.0.33, 7.1.0 - 7.1.25, 7.2.0 - 7.2.33, 7.3.0 - 7.3.33, 7.4.0 - 7.4.33, 8.0.0 - 8.0.30, 8.1.0 - 8.1.33, 8.2.0 - 8.2.29, 8.3.0 - 8.3.26, 8.4.1 - 8.4.13
array(2) { ["a"]=> int(666) [0]=> int(555) }
preferences:
192.11 ms | 408 KiB | 5 Q