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iOS Intermediate Swift 2 Extensions and Protocols Extending a Native Type

Posted by Nehemiah Reese
Nehemiah Reese
17,692 Points

Can anybody help with the "Extend a Native Type Challenge?" Here is my code:

extension String { func add(i: Int) -> Int? { if self.intValue { return self.intValue + i } else { return nil } } }

types.swift 
// Enter your code below

extension String {
    func add(i: Int) -> Int? {
        if self.intValue {
            return self.intValue + i
        } else {
            return nil
        }
    }
}

1 Answer

Greg Kaleka
Greg Kaleka
39,021 Points
Greg Kaleka
Greg Kaleka
39,021 Points

Hi Nehemiah,

You're close, but there are two issues with your code:

  1. Swift Strings don't have a property intValue like NSStrings do.
  2. In Swift you can't use an if statement like that - you could say if thingThatMightBeNil != nil, but using guard or if let is better

Here's a solution using if let:

// Enter your code below
extension String {
    func add(i: Int) -> Int? {
        if let numberFromString = Int(self) {
            return numberFromString + i
        } else {
            return nil
        }
    }
}

and here's one using guard, which I prefer in this case:

// Enter your code below
extension String {
    func add(i: Int) -> Int? {
        guard let numberFromString = Int(self) else {
            return nil
        }
        return numberFromString + i
    }
}

Let me know if any of this doesn't make sense!

Happy coding :thumbsup:

-Greg

Nehemiah Reese
Nehemiah Reese
17,692 Points

Thanks! Makes perfect sense now. I was looking into the NSString documentation lol. I'm sort of a newbie at programming still polishing up.

Greg Kaleka
Greg Kaleka
39,021 Points
Greg Kaleka
Greg Kaleka
39,021 Points

Awesome - glad I could help!