Type alias OnlyIndexes<E, I>
OnlyIndexes<E, I>: I extends number ? OnlyIndexes<E, [I]> : I extends readonly [infer Head extends number, ...(infer Tail extends RoArray<number>)] ? E[Head] extends undefined ? OnlyIndexes<E, Tail> : [E[Head], ...OnlyIndexes<E, Tail>] : []