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<?php $arr1 = array(); $arr2 = array(); $arr1[-1] = 5; $arr2['-1'] = 5; var_dump($arr1, $arr2);
Output for 4.3.3 - 4.3.11, 4.4.0 - 4.4.9, 5.0.0 - 5.0.5, 5.1.0 - 5.1.6, 5.2.0 - 5.2.17, 5.3.0 - 5.3.29, 5.4.0 - 5.4.45, 5.5.0 - 5.5.37, 5.6.0 - 5.6.28, 7.0.0 - 7.0.20, 7.1.0 - 7.1.33, 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 - 8.1.28, 8.2.0 - 8.2.18, 8.3.0 - 8.3.6
array(1) { [-1]=> int(5) } array(1) { [-1]=> int(5) }
Output for 4.3.0 - 4.3.2
array(1) { [-1]=> int(5) } array(1) { ["-1"]=> int(5) }

preferences:
286.24 ms | 401 KiB | 396 Q