Naive String.toDouble() in swift

gistfile1.txt

extension String {
    func toDouble() -> Double? {
        var formatter = NSNumberFormatter()
        let number = formatter.numberFromString(self)
        if number == nil {
            return nil
        }
        return number.doubleValue
    }
}

if let d = "123.1".toDouble() {
    println(d)
}

This doesn't compile in Swift 1.0. It just needs a minor change though:

func toDouble() -> Double? {
    var formatter = NSNumberFormatter()
    let number = formatter.numberFromString(self)
    return number?.doubleValue
}