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<?php $a1 = ['foo' => 'bar', 'bar' => 'baz']; $a2 = ['baz' => 'foo']; $a3 = []; var_dump(array_merge($a1, $a2)); var_dump(array_merge($a1, $a3));

preferences:
35.73 ms | 402 KiB | 5 Q