Xtykutl

In my application written in Swift 4.2 I have the following code:

let arrayOfIntegers = [2, 1, 9, 5, 4, 6, 8, 7]

let unknownLowerBound = 4

let unknownUpperBound = 20

let closedRange = ClosedRange<Int>(uncheckedBounds: (lower: unknownLowerBound,

                                                     upper: unknownUpperBound))

let subRange = arrayOfIntegers[closedRange]

subRange.forEach { print($0) }

As you can guess when I am running this code I receive the following error: Fatal error: Array index is out of range. I want to prevent it.

You can check if the range of valid array indices “clamped” to
the given closed range is equal to that range:

let array = [1, 2, 3, 4, 5, 6, 7, 8]

let closedRange = 4...20

if array.indices.clamped(to: Range(closedRange)) == Range(closedRange) {

    let subArray = array[closedRange]

    print(subArray)

} else {

    print("closedRange contains invalid indices")

}

Or, equivalently:

if array.indices.contains(closedRange.lowerBound)

    && array.indices.contains(closedRange.upperBound) {

    // ...

}