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

John Wilcox
John Wilcox
4,233 Points
Posted by John Wilcox
John Wilcox
4,233 Points

Extra argument in call?

Hi, I'm getting an 'extra argument author in call' error. I can't figure out why - author is unwrapped in the guard statement. The memberwise init does call for author. Any suggestions?

optionals.swift 
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
      } 

      let price = dict["price"]
      let pubDate = dict["pubDate"]

      Book(title: title, author: author, price: price, pubDate: pubDate)
    }

}

1 Answer

David Papandrew
David Papandrew
8,386 Points
David Papandrew
David Papandrew
8,386 Points

Hi John,

You want to bind the values passed in as arguments to the init method to the Book properties. There's also an extraneous line of code in the init method with a class declaration and parameters. You should remove that.

Here's the corrected code:

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"]
    }
}
John Wilcox
John Wilcox
4,233 Points
John Wilcox
John Wilcox
4,233 Points

Bah, you're right. I see that I should have just assigned to the parameters directly. Thanks - sometimes I truly think I'm dyslexic when it comes to code.

What do you mean when you said "There's also an extraneous line of code in the init method with a class declaration and parameters." I see I can omit the underscore before the word dict. Otherwise however, to my eyes our guard statements look alike.

David Papandrew
David Papandrew
8,386 Points
David Papandrew
David Papandrew
8,386 Points

Hi John,

The line I was referring to is this one in the init method:

Book(title: title, author: author, price: price, pubDate: pubDate)

But maybe that was how you were trying to assign the parameters. Either way, good luck!