Floyd Resler Floyd Resler - 23 days ago 10
Swift Question

String subscripting error

I just converted to Swift 4 and am now getting the following error:
Cannot subscript a value of type 'String.UnicodeScalarView' with an index of type 'CountableRange' (aka 'CountableRange')

The lines of code are:

extension AppInvite.PromoCode {
fileprivate static func truncate(string: String) -> String {
let validCharacters = CharacterSet.alphanumerics
let cleaned = string.unicodeScalars.filter {

let range = 0 ..< min(10, cleaned.count)
let characters = cleaned[range].map(Character.init)
return String(characters)

How can I correct it?

Answer Source

You are using a CountableRange<Int> but to access to the characters of a String you must use CountableRange<String.Index>:

let range = cleaned.startIndex..<min(cleaned.index(cleaned.startIndex, offsetBy: 10), cleaned.endIndex)

That's because in Swift, String type has an index type of String.Index and not of Int.