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iOS

Posted by Roger Panella
Roger Panella
5,968 Points

Question about code challenge: Array[0] isn't optional?

I was able to write code that passed the code challenge, but looking at Xcode errors I saw as I was doing it brought up a question. This is my passing code:

let movieDictionary = ["Spectre":
                        ["cast":
                            ["Daniel Craig", "Christoph Waltz", "Léa Seydoux", "Ralph Fiennes", "Monica Bellucci", "Naomie Harris"]
                        ]
                      ]

var leadActor = ""


if let movieTitle = movieDictionary["Spectre"],
    let movieCast = movieTitle["cast"] {
       leadActor = movieCast[0]
       print(leadActor)
}

However, if I try to make "leadActor = movieCast[0]" a part of the "if let", I get the error: "Initializer for conditional binding must have Optional type, not 'String'" To fix it, I moved the first curly bracket in the if/let to be after the "let movieCast" line, removed "let" from the next line.

My question is: Isn't is possible that movieCast[0] would be nil? And, if I looked for the array value [0] of an empty array, wouldn't that cause a crash/error?

Roger Panella
Roger Panella
5,968 Points

I'm not sure why this isn't connected to the video I asked the question on. I was on the questions section for that video, then clicked "Ask", so this probably doesn't make sense out of context.

I'm referring to the code challenge after the Optional Binding video in "Swift 2.0 Enumerations and Optionals"

1 Answer

Steven Deutsch
Steven Deutsch
21,046 Points
Steven Deutsch
Steven Deutsch
21,046 Points

Hey Roger Panella,

Great question. When you subscript an array the value returned is not an optional. This differs from dictionaries. Whenever you look up a value in a dictionary using a key, the value is always returned as an optional. To further answer your question, yes, anytime you subscript an array with an index that is out of range - you will get a run time error and your program will crash.

let movieDictionary = ["Spectre": ["cast": ["Daniel Craig", "Christoph Waltz", "Léa Seydoux", "Ralph Fiennes", "Monica Bellucci", "Naomie Harris"]]]

var leadActor: String = ""

// Enter code below

if let movie = movieDictionary["Spectre"],
    let cast = movie["cast"] {
        leadActor = cast[0]
}

Good Luck!