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iOS Intermediate Swift 2 Extensions and Protocols Extending a Native Type

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

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
        }
    }     
}