János János - 5 months ago 107
Swift Question

How to use substringToIndex in Swift?

I get compiler error at this line:

UIDevice.currentDevice().identifierForVendor.UUIDString.substringToIndex(8)


Type 'String.Index' does not conform to protocol 'IntegerLiteralConvertible'

My intention is to get the substring, but how?

Answer

In Swift, String indexing respects grapheme clusters, and an IndexType is not an Int. You have two choices - cast the string (your UUID) to an NSString, and use it as "before", or create an index to the nth character.

Both are illustrated below :

However, the method has changed radically between versions of Swift. Read down for later versions...

Swift 1
let s: String = "Stack Overflow" let ss1: String = (s as NSString).substringToIndex(5) // "Stack" //let ss2: String = s.substringToIndex(5)// 5 is not a String.Index let index: String.Index = advance(s.startIndex, 5) let ss2:String = s.substringToIndex(index) // "Stack"

CMD-Click on substringToIndex confusingly takes you to the NSString definition, however CMD-Click on String and you will find the following:

extension String : Collection {
    struct Index : BidirectionalIndex, Reflectable {
        func successor() -> String.Index
        func predecessor() -> String.Index
        func getMirror() -> Mirror
    }
    var startIndex: String.Index { get }
    var endIndex: String.Index { get }
    subscript (i: String.Index) -> Character { get }
    func generate() -> IndexingGenerator<String>
}

Swift 2
As commentator @DanielGalasko points out advance has now changed...

let s: String = "Stack Overflow"
let ss1: String = (s as NSString).substringToIndex(5) // "Stack"
//let ss2: String = s.substringToIndex(5)// 5 is not a String.Index
let index: String.Index = s.startIndex.advancedBy(5) // Swift 2
let ss2:String = s.substringToIndex(index) // "Stack"

Swift 3
In Swift 3, it's changed again:

let s: String = "Stack Overflow"
let ss1: String = (s as NSString).substring(to: 5) // "Stack"
let index: String.Index = s.index(s.startIndex, offsetBy: 5)
var ss2: String = s.substring(to: index) // "Stack"