Swift: How to convert String to UInt?

Question

According to Swift - Converting String to Int, there\'s a String method toInt().

But, there\'s no toUInt() method. So, how to conv

Answer 1

Please, for the love of not crashing, don’t use ! to do this.

It’s easy to tack a map on the end of toInt to convert it to an optional UInt:

let str = "4"
let myUInt = str.toInt().flatMap { $0 < 0 ? nil : UInt($0) }

then use the usual unwrapping techniques on myUInt.

And if you find yourself doing this a lot:

extension String {
    func toUInt() -> UInt? {
        return self.toInt().flatMap { $0 < 0 ? nil : UInt($0) }
    }
}

let str = "-4"
if let myUInt = str.toUInt() {
    println("yay, \(myUInt)")
}
else {
    println("nuh-uh")
}

edit: as @MartinR points out, while safe, this doesn’t extract the full range of possible values for a UInt that Int doesn’t cover, see the other two answers.