Lost on this question. How do I create a failable Init?

You are getting close. The dictionary parameter is correct, as well as the guard statement. However, you still need to initialize the book properties. So far you asked the dictionary for the different Strings, but did not use them for initialization.

Think of the guard statement as an early exit from the initializer method. If the necessary information can not retrieved from the dictionary, the guard statement ensures, that the initializer returns nil. But otherwise, all book properties have to be initialized by the end of the method.

This said, make sure to assign the values retrieved from the dictionary to the book properties. Do not return nil outside of the guard statement a second time.

As a reminder, take this as an example for initializing the author property:

self.author = author

I think this challenge is hard, too. The failable initializer could be implemented with the help of a guard statement.

But first things first. Instead of a list of four different (optional) strings, the parameter of the initializer should be of type [String: String] and named dict. Next, you can use the provided keys to retrieve the individual values for the different properties.

All values that are retrieved from the dictionary are of type Optional(String), but two struct properties are of type String. These two are good candidates to check for existence with the help of a guard statement. If the dictionary does not contain all the values needed, a failable initializer should return nil.

I hope this helps. Please ask again, if you still have questions.

stuck on this as well. why doesn't this work:

struct Book {

let title: String

let author: String

let price: String?

let pubDate: String?

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

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

    }

    let price = dict["price"], pubDate = dict["pubDate"]
    return nil

}

}

got it! and understand it a little better now too. in another post i found an answer using if statements but this seems way better.

I did the challenge, but I don't understand why the init method only accepts one arguement when we have 4 properties to be set. When trying to create an instance of the Book struct, we can only set one property, and it returns nil because the other properties are empty, yes?

let someBook = Book(dict: ["title":"potter"]) // prints nil in the playground

How can I add more to the someBook, to make it return all properties with values?