Welcome to the Treehouse Community

Want to collaborate on code errors? Have bugs you need feedback on? Looking for an extra set of eyes on your latest project? Get support with fellow developers, designers, and programmers of all backgrounds and skill levels here with the Treehouse Community! While you're at it, check out some resources Treehouse students have shared here.

Looking to learn something new?

Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and join thousands of Treehouse students and alumni in the community today.

Start your free trial

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

Patrick Duhamel
Patrick Duhamel
5,786 Points
Posted by Patrick Duhamel
Patrick Duhamel
5,786 Points

Failable initializer task is missing something, but Playground or Preview mode doesn't give me a hint on the issue...

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

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

}

optionals.swift 
struct Book {
    let title: String
    let author: String
    let price: String?
    let pubDate: String?

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

}

1 Answer

Joshua Hawthorne
Joshua Hawthorne
18,523 Points
Joshua Hawthorne
Joshua Hawthorne
18,523 Points

Notice that "price" and "pubDate" in the Book struct are actually optionals. These values are allowed to be nil. In other words, price and pubDate can both be nil, and as long as title and author are valid we can create the instance of the struct. Your code should like like this (note that I am using guard statements, not if-let): 

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


    init?(dict: [String : String]) {

        guard let title = dict["title"] else { return nil }
        guard let author = dict["author"] else { return nil }

        if let p = dict["price"] {
            self.price = p
        } else {
            self.price = nil
        }

        if let pubDate = dict["pubDate"] {
            self.pubDate = pubDate
        } else {
            self.pubDate = nil
        }

        self.title = title
        self.author = author

    }

}