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iOS Intermediate Swift 2 Extensions and Protocols Extending a Native Type

Kittipol Munkatitum
Kittipol Munkatitum
13,074 Points

I can't submit this challenge

this is my code but when I submit I can't pass this challenge. Could you give some hint for this challenge

extension String{

func add(number: Int) -> Int  {
    if let unwrapped:Int = Int(self) ?? nil{
        return unwrapped + number
    } else {
        return 0
    }
}

}

types.swift
// Enter your code below
extension String{


    func add(number: Int) -> Int  {
        if let unwrapped:Int = Int(self) ?? nil{
            return unwrapped + number
        } else {
            return 0
        }
    }

}