Shift elements in array by index

by

You can use ranged subscripting and concatenate the results. This will give you what you’re looking for, with names similar to the standard library:

extension Array {
    func shiftRight(var amount: Int = 1) -> [Element] {
        guard count > 0 else { return self }
        assert(-count...count ~= amount, "Shift amount out of bounds")
        if amount < 0 { amount += count }  // this needs to be >= 0
        return Array(self[amount ..< count] + self[0 ..< amount])
    }

    mutating func shiftRightInPlace(amount: Int = 1) {
        self = shiftRight(amount)
    }
}

Array(1...10).shiftRight()
// [2, 3, 4, 5, 6, 7, 8, 9, 10, 1]
Array(1...10).shiftRight(7)
// [8, 9, 10, 1, 2, 3, 4, 5, 6, 7]

Instead of subscripting, you could also return Array(suffix(count - amount) + prefix(amount)) from shiftRight().

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