NSRange to Range

Question

How can I convert NSRange to Range in Swift?

I want to use the following UITextFieldDelegate method:

Answer 1

Here's my best effort. But this cannot check or detect wrong input argument.

extension String {
    /// :r: Must correctly select proper UTF-16 code-unit range. Wrong range will produce wrong result.
    public func convertRangeFromNSRange(r:NSRange) -> Range {
        let a   =   (self as NSString).substringToIndex(r.location)
        let b   =   (self as NSString).substringWithRange(r)

        let n1  =   distance(a.startIndex, a.endIndex)
        let n2  =   distance(b.startIndex, b.endIndex)

        let i1  =   advance(startIndex, n1)
        let i2  =   advance(i1, n2)

        return  Range(start: i1, end: i2)
    }
}

let s   =   "