Answer by Leo Dabus for How to remove special characters from string in Swift 2?

If you need to keep only ascii printable characters in a string you can just filter them checking if their unicodeScalar values are ascii:

extension Character {
    var isAscii: Bool {
        return unicodeScalars.allSatisfy { $0.isASCII }
    }
}

extension RangeReplaceableCollection where Self: StringProtocol {
    var asciiPrintable: Self {
        return filter { $0.isAscii }
    }
}

let string = "cafe\u{301}"
let asciiPrintable = string.asciiPrintable
print(asciiPrintable)  // "caf"