how do extensions work exactly?

Hey Todd Stacy,

We use an extension when we want to add extra functionality to a type that already exists. This could be a custom type you created or one that is provided in one of Apple's Frameworks. In this challenge, we are being asked to override the String type.

The challenge wants us to create a method called "add" as an extension to the String type. This method will take a single parameter of type Int and have a return type of Int?. Since we are going to be performing a mathematical operation on a String, we need to be able to return nil if the string can't be converted to an Integer. That is why our return type is optional.

Inside the methods body, we first need to check if the string we are calling this method on can be converted successfully to an integer. If it can, we will perform the operation of adding the value we pass in when calling this method to the value of the converted string. If it can't be converted from String to Int, well, we will return nil.

It makes sense to use a guard statement here to achieve this, because we want to make sure that the string can be converted to an integer before we continue execution of this method. If this isn't the case, we will jump into the else block and exit the scope of the function immediately.

// Enter your code below

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

    return conversion + n
  }
}

Good Luck