if let culprit = findApt("505"){}

Yeah, this is a little confusing. Let's walk through it.

func findApt (aptNumber : String) -> String {
    let aptNumbers = ["101","202","303","404"]
    for tempAptNumber in aptNumbers {
        if ( tempAptNumber == aptNumber) {
            return aptNumber
        }
    }
}

Let's first understand what happens when you are passing "505" into the above function where we have declared the function to return a String type. So in the this scenario your conditional return will never happen. This is what causes the compile error.

So what we could do is have a return outside of the for loop that will return the empty string as the video described. But as described this could break other things, such as with the bool evaluation example.

So this is where the nil return comes into it. But remember, you can't assign nil to a String type. You need to have an optional String type (that is String?). So your function can be defined now with the optional return. Looks like this now.

func findApt (aptNumber : String) -> String? {
    let aptNumbers = ["101","202","303","404"]
    for tempAptNumber in aptNumbers {
        if ( tempAptNumber == aptNumber) {
            return aptNumber
        }
    }

    return nil

}

In this case we are return a nil with your 505. So if you assign that to a value like the example given, but you always take care with with functions that can return nil and safely unwrap it. Remember, unwrapping is putting the ! on the end of your value to say "I know this could be nil and am ready for it!". So you use the function like this.

if let culprit = findApt("505") {
    print("Apt Found")
}

This is the "safety" that is built into swift. You are making a function that you know can return a nil value. You are using that function in a way that checks to see if nil is returned (the "if let" example). That way you will never have your code crash because it expected data to be where there was none.

So, in short, these are your rules.

• If your function has a return value, all possible outcomes must return a value.
• If your function has outcomes that have no value to return use nil with an optional return (the ?).
• If you are using a function that could return a nil value (an optional return) you need to unwrap it (the !).
• If you are unwrapping something always do it safely (such as with the "if let" conditional).

I hope this helps. :)

Oh, are you positive about that? In that case, this makes so much more sense! Thanks so much!