Generate random alphanumeric string in Swift

Question

How can I generate a random alphanumeric string in Swift?

Answer 1

Loop free, though it is limited to 43 characters. If you need more, it can be modified. This approach has two advantages over solely using a UUID:

1. Greater Entropy by using lower case letters, as UUID() only generates upper case letters
2. A UUID is at most 36 characters long (including the 4 hyphens), but only 32 characters long without. Should you need something longer, or not want hyphens included, the use of the base64EncodedString handles this

Also, this function makes use of a UInt to avoid negative numbers.

 func generateRandom(size: UInt) -> String {
        let prefixSize = Int(min(size, 43))
        let uuidString = UUID().uuidString.replacingOccurrences(of: "-", with: "")
        return String(Data(uuidString.utf8)
            .base64EncodedString()
            .replacingOccurrences(of: "=", with: "")
            .prefix(prefixSize))
    }

Calling it in a loop to check output:

for _ in 0...10 {
    print(generateRandom(size: 32))
}

Which produces:

Nzk3NjgzMTdBQ0FBNDFCNzk2MDRENzZF
MUI5RURDQzE1RTdCNDA3RDg2MTI4QkQx
M0I3MjJBRjVFRTYyNDFCNkI5OUM1RUVC
RDA1RDZGQ0IzQjI1NDdGREI3NDgxM0Mx
NjcyNUQyOThCNzhCNEVFQTk1RTQ3NTIy
MDkwRTQ0RjFENUFGNEFDOTgyQTUxODI0
RDU2OTNBOUJGMDE4NDhEODlCNEQ1NjZG
RjM2MTUxRjM4RkY3NDU2OUFDOTI0Nzkz
QzUwOTE1N0U1RDVENDE4OEE5NTM2Rjcy
Nzk4QkMxNUJEMjYwNDJDQjhBQkY5QkY5
ODhFNjU0MDVEMUI2NEI5QUIyNjNCNkVF