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iOS Swift 2.0 Enumerations and Optionals Introduction to Optionals Initializing Optional Values

Posted by Peyton Weatherford
Peyton Weatherford
5,515 Points

I really need help.

I tried the next code challenge, and this is what I came up with. But, if i try to use this code the whole thing lights up like a Christmas tree. Can anybody please help explain how I messed up this terribly?

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"]
        return? Book(title: title, author: author, price: price, pubDate: pubDate)
        }
         else {
      return nil
    }
}

1 Answer

Oliver Duncan
Oliver Duncan
16,642 Points
Oliver Duncan
Oliver Duncan
16,642 Points

There are a few problems with this, let's take a look.

  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"] // Here's where you need to assign variables to your struct, not create new variables 
        return? Book(title: title, author: author, price: price, pubDate: pubDate) // You don't need a question mark after the return statement. Also, initialization methods don't return a value(except for failable inits, which can return nil), they just assign variables.
        }
         else {
      return nil
    }
}

With these issues in mind, let's see the proper way to initialize the Book struct with a failable initializer.

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"] {
      // Assign stored properties here, don't return anything
      self.title = title
      self.author = author
      self.price = dict["price"]
      self.pubDate = dict["pubDate"]
    } else {
      return nil // Initialization fails if title or author is nil
    }
  }

}

Here's another way of writing the same method, this time a guard statement.

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"]
}