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

Aananya Vyas
Aananya Vyas
20,157 Points
Posted by Aananya Vyas
Aananya Vyas
20,157 Points

cant understand what to do

initialised all prop of struct ... put the guard stmt... what else?!

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

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



}

3 Answers

Jorge Solana
Jorge Solana
6,064 Points
Jorge Solana
Jorge Solana
6,064 Points

You have a blank space between self. and author. Author is a property of self, so it needs to be typed together or compiler will not understand.

self.author = author

I already suggest you try to keep your code clean. I mean, try to put your parenthesis and other marks ("[", "{", "(", etc.) in position so you can easily get where some condition, class or whatever ends and finishes.

Example:

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 it helps!

Jorge Solana
Jorge Solana
6,064 Points
Jorge Solana
Jorge Solana
6,064 Points

Hi Aananya!

Since it's a title bit confusing, I'm going to c&p some documentation text:

It is sometimes useful to define a class, structure, or enumeration for which initialization can fail. This failure might be triggered by invalid initialization parameter values, the absence of a required external resource, or some other condition that prevents initialization from succeeding.

A failable initializer creates an optional value of the type it initializes. You write return nil within a failable initializer to indicate a point at which initialization failure can be triggered.

What I understand it does is that the initializer spect the properties as optionals, like everything could go wrong. So since price and pubDate are already optionals, we need to add some control to the author and title properties. We do so using the guard let statement, so if anything goes wrong there, we break the current scope of the init method (by returning nil). So final code will be like this:

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

Hope it helps and happy coding!

Aananya Vyas
Aananya Vyas
20,157 Points
Aananya Vyas
Aananya Vyas
20,157 Points 
 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"]
}



}```
Aananya Vyas
Aananya Vyas
20,157 Points
Aananya Vyas
Aananya Vyas
20,157 Points

i understood but..still isn't working...