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

Monzer Selim
PLUS
Monzer Selim
Courses Plus Student 3,849 Points
Posted by Monzer Selim
Monzer Selim
Courses Plus Student 3,849 Points

how to Make sure that the initializer returns a valid instance given a valid dictionary?

can u help me with that ?

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 }
        self.price = dict["price"]
        self.pubDate = dict["pubDate"]

        return nil
    }

}

1 Answer

Steven Deutsch
Steven Deutsch
21,046 Points
Steven Deutsch
Steven Deutsch
21,046 Points

Hey Monzer Selim,

Remember that the job of the initializer is to make sure that all of the instance's properties have values. You're on the right track, you just need to finish assigning the values you unwrapped with the guard statement to their properties.

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

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

         /* Looking up values in dict w/ key always returns optional.
             Here we unwrap because title & author cannot be optional. */

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

        /* We now assign those non-optional values to their 
            corresponding non-optional properties */

        self.title = title
        self.author = author

        // These two properties accept optional values

        self.price = dict["price"]
        self.pubDate = dict["pubDate"]
    }
}

You may also notice that I removed the double return nil statement. We only want to return nil if we are unable to optional bind one of the values that we need to assign to the instance's non-optional property.

Good Luck