'subscript' is unavailable: cannot subscript String with a CountableClosedRange, see the documentation comment for discussion

Question

In Swift 4, I\'m getting this error when I try to take a Substring of a String using subscript syntax.

\'subscript\' is unavaila

Answer 1

1. If you want to use subscripts on Strings like "palindrome"[1..<3] and "palindrome"[1...3], use these extensions.

Swift 4

extension String {
    subscript (bounds: CountableClosedRange) -> String {
        let start = index(startIndex, offsetBy: bounds.lowerBound)
        let end = index(startIndex, offsetBy: bounds.upperBound)
        return String(self[start...end])
    }

    subscript (bounds: CountableRange) -> String {
        let start = index(startIndex, offsetBy: bounds.lowerBound)
        let end = index(startIndex, offsetBy: bounds.upperBound)
        return String(self[start..

Swift 3

For Swift 3 replace with return self[start...end] and return self[start...

2. Apple didn't build this into the Swift language because the definition of a 'character' depends on how the String is encoded. A character can be 8 to 64 bits, and the default is usually UTF-16. You can specify other String encodings in String.Index.

This is the documentation that Xcode error refers to.

More on String encodings like UTF-8 and UTF-16