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iOS Swift 2.0 Enumerations and Optionals Introduction to Optionals Recap on Optionals

Berry Loeffen
Berry Loeffen
4,303 Points
Posted by Berry Loeffen
Berry Loeffen
4,303 Points

Adding a function to the next challenge.

Adding the function bookDetails to the struct. Is this the way to do it or is there a shorter version possible? I don't think a Guard statement can be used here, so I used "else if let" statements. Any ideas? or is there just no shorter way to do this?

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"]
    }
    func bookDetails() -> String {

        if let price = price, let pubDate = pubDate {
            return "\(title), \(author), \(price), \(pubDate)"
        }

        else if let price = price {
            return "\(title), \(author), \(price)"
        }
        else if let pubDate = pubDate {
            return "\(title), \(author), \(pubDate)"
        } else {
            return "\(title), \(author)"}
    }    
 }
Greg Kaleka
Greg Kaleka
39,021 Points
Greg Kaleka
Greg Kaleka
39,021 Points

Just came across this. Gianpiero's answer is very elegant. Just to point this out, though - you definitely could use guard. It's a bit sticky, though. I'll show it to you "clean" and then walk through the logic. It's not the most elegant thing... but it works!

cleanVersion.swift 
func bookDetails() -> String {

    guard let price = price else {
        guard let pubDate = pubDate else {
            return "\(title) by \(author)"
        }
        return "\(title) by \(author), published \(pubDate)"
    }

    guard let pubDate = pubDate else {
        return "\(title) by \(author) for \(price)"
    }

    return "\(title) by \(author), published \(pubDate). On sale for \(price)"

}
annotatedVersion.swift 
// There are 4 possibilities
// 1. price=nil && pub=nil
// 2. price=nil && pub!=nil
// 3. price!=nil && pub=nil
// 4. price!=nil && pub!=nil

func bookDetails() -> String {
    guard let price = price else {
        // 1. or 2.
        guard let pubDate = pubDate else {
            // 1. price=nil && pub=nil
            return "\(title) by \(author)"
        }
        // 2. price=nil && pub!=nil
        return "\(title) by \(author), published on \(pubDate)"
    }
    // 3. or 4.
    guard let pubDate = pubDate else {
        // 3. price!=nil && pub=nil
        return "\(title) by \(author) for \(price)"
    }
    // 4. price!=nil && pub!=nil
    return "\(title) by \(author), published on \(pubDate) for \(price)"
}

1 Answer

gianpierovecchi
gianpierovecchi
15,043 Points

You should start concatenating the non optional string and then add the optional.. like:

func bookDetails() -> String {
   var details = "\(title), \(author)"
   if let price = price {
      details += ", \(price)"
   }     
   if let pubDate = pubDate {
      details += ", \(pubDate)"
   }
   return details
}

Shortened with ternary operator:

func bookDetails() -> String {
   return "\(title), \(author)" + (price != nil ? ", \(price)" : "") + (pubDate != nil ? ", \(pubDate)" : "")
}

But if you want a glimpse about how fun is the language, you can use closures and array methods to do the work for you:

func bookDetails() -> String {
   return [title, author, price, pubDate].flatMap{$0}.joinWithSeparator(", ")
}

flatMap is a filtering function that returns an Array without the nil values (the parameter $0 in curly braces is a shortened syntax of a closure, if you didn't study it yet you will be surprised), and JoinWithSeparator in pretty obvious.

Have fun programming! :)