Welcome to the Treehouse Community

Want to collaborate on code errors? Have bugs you need feedback on? Looking for an extra set of eyes on your latest project? Get support with fellow developers, designers, and programmers of all backgrounds and skill levels here with the Treehouse Community! While you're at it, check out some resources Treehouse students have shared here.

Looking to learn something new?

Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and join thousands of Treehouse students and alumni in the community today.

Start your free trial

iOS Intermediate Swift 2 Extensions and Protocols Extending a Native Type

Mit Sengupta
Mit Sengupta
13,823 Points
Posted by Mit Sengupta
Mit Sengupta
13,823 Points

What is wrong with my code?

It seems to work in the play ground. Here's the code: 

extension String {
    func add(num: Int) -> Int {
        if num == num {
            return num + num
        }
        else {
            return "nil"
        }
    }     
}
"8".add(8)
types.swift 
// Enter your code below

extension String {
    func add(num: Int) -> Int {
        if num == num {
            return num + num
        }
        else {
            return 0
        }
    }

}

"8".add(8)

1 Answer

jcorum
jcorum
71,830 Points
jcorum
jcorum
71,830 Points

You need to use self to get the String that you will try to add to your num. Also, since your function can return nil you need to make the return type Int?, i.e., an optional. Then you need to test to see if self does indeed contain an Int, using optional binding:

extension String {
    func add(num: Int) -> Int? {
        if let n = Int(self) {
            return n + num
        }
        else {
            return nil
        }
    }     
}