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iOS Intermediate Swift Extensions and Protocols Extending a Native Type

Arius Eich
Arius Eich
2,769 Points
Posted by Arius Eich
Arius Eich
2,769 Points

Using extensions

I do not understand how to execute the question as well as how to execute it. Are they asking to add an integer to a string as in just place it in there or do they want the number added to the number already in the string? This is the objective: Your task is to extend the String type and add a method that lets you add an integer value to the string. For example: "1".add(value: 2) If the operation is possible, return an integer value. If the string does not contain an integer and you cannot add to it then return nil. Thank you for any help!

types.swift 
// Enter your code below
extension String {
 var add: var(value: string) {
   if value == 0 {
    return nil
     if else {
      return  
     }
   }
 }
}

1 Answer

Magnus Hållberg
Magnus Hållberg
17,232 Points
Magnus Hållberg
Magnus Hållberg
17,232 Points

They are asking you to extend the String type with a method that checks if the string is a number (specifically an Int), if it is you are supposed to add that to the input from the method. Hope that makes sense. Since the method should return nil if the string is not an Int the return must be optional. This is one way of solving it. 

extension String {
    func add(value: Int) -> Int? {
        // check if the string is an Int
        if let stringInt = Int(self) {
            // if the string is an Int, add the value from the method input and return it
            return stringInt + value
        } else {
            // if its not an Int, return nil
            return nil
        }
    }
}

Using the extension could look something like this. 

let myString = "2"
myString.add(value: 2)
// myString is now of the type optional Int with the value 4

let myString2 = "Hi"
mystring2.add(value: 2)
// myString2 is now of the type optional Int with the value nil

Hope this helps