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<?php $a[0] = 0; $a[1] = 1; unset($a[1]); var_dump(array_is_list($a)); $a[] = 2; var_dump(array_is_list($a));
Output for 8.2.31 - 8.2.35, 8.3.0 - 8.3.36, 8.4.1 - 8.4.27, 8.5.0 - 8.5.11
bool(true) bool(false)

preferences:
36.88 ms | 1507 KiB | 8 Q