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iOS Enumerations and Optionals in Swift Introduction to Optionals Initializing Optional Values

Anatolii Tcai
Anatolii Tcai
2,401 Points
Posted by Anatolii Tcai
Anatolii Tcai
2,401 Points

Do not really understand the task. So I create a failable initializer using init?, but how to retrieve the values?

The task is to create a failable initializer using a dictionary of type [String : String] as input. It also should initialize all the stored properties. So how do I do that?

optionals.swift 
struct Book {
    let title: String
    let author: String
    let price: String?
    let pubDate: String?
    init?(dict: [String : String]) {
        return nil
    }
}
Anthony Lafont
Anthony Lafont
17,075 Points
Anthony Lafont
Anthony Lafont
17,075 Points

Hi Anatoli, that's a tough one ;) The purpose of an initializer is to initiate all stored properties, in your response, nothing is initialized, that's why it doesn't work. To initialize them, you have to be sure that a least the two first properties exist, otherwise the initializer should return nil (as it's failable). The best way is to use a guard let statement. Here is how I've done:

struct Book {
    let title: String
    let author: String
    let price: String?
    let pubDate: String?

    init?(dict: [String : String]){
        guard let title = dict["title"], let author = dict["author"] else { return nil }
        self.title = title
        self.author = author
        self.price = dict["price"]
        self.pubDate = dict["pubDate"]
    }

}

Hope that helps!