Help please.. Getting frustrated with this code challenge

Hey Simon,

First of all, I just want to tell you that this is not easy to understand at all. So just take a deep breath and keep going.

This is my solution. Not sure if the solution you copied is like mine but in any case I think that might help you.

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"]
    }
}

1)We haven't learned about using init? methods before yet we're expected to do this in the challenge? Yeah, at this point we hadn't indeed. They usually do it just to drive us crazy =D. It is hard but in the end it is helpful. As they always say, developers need to learn new things all the time. But trust me I get your point.

2)Anyway. How do I retrieve keys from the dictionary when there is no dictionary. It makes no sense. So, first of all, you HAVE a dictionary because you always HAVE to pass a dictionary when creating an instance of Book, what you may not have is the key 'title' or 'author' or 'price' or 'pubDate'. But in case the dictionary doesn't have the key 'price' or 'pubDate', this will not be a problem when creating a Book because 'price' or 'pubDate' are optional and as they are optional they can have nil assigned to them.

Let's see an example:

Let's suppose there is an app where users need to fill in a form with information about a book. The user has to type the 'title' and 'author' and it is optional to type the price and pubDate. In other to create the book with the users' input I would have to do something like that.

var dict = [String : String]
dict["titel"] = bookLabel.text
dict["author"] = authorLabel.text

var book = Book(dic)

Would that work? No it wouldn't. Why?

When you pass this dict to the init? of the book, it checks if there is a key 'title' and if there is this key then it assigns its value to the title constant. Don't know if you noticed, but when I created the dict I made a typo and created a key TITEL not 'title'. It is a silly example but trust me it may happen.

Another example may be that I was getting this dictionary from a REST API(Don't know if you are familiar with that but if you are not just think about it as a service on the internet that will return you a dictionary with books). This could also fail. The first time you try to create a dictionary with the information from the API, you would write something like that.

var dict = [String : String]
dict["title"] = dictFromAPI["title"]
dict["author"] = dictFromAPI["author"]

var book = Book(dic)

So, ok that would work.

But it may not work in the future.

The guys that created the api, were indeed returning a dictionary that had those keys 'title' and 'author' but for some reason they decided to change and now instead of returning a dict with a key called 'title' they are returning a key called 'titleBook'.

Hope this helps Simon, Good luck!

Ohhh, try this way..

var dictFromTheAPI = [String: String]() // I forgot to add the parentheses
dictFromTheAPI["title"] = "iOS"
dictFromTheAPI["author"] = "Simon"
var dict = [String : String]()
dict["title"] = dictFromTheAPI["title"] //Retrieving the value of the key 'title' from the 'dictFromTheAPI' thats equal to 'iOS' and assigning this value to the key 'title' of the 'dict'.
dict["author"] = dictFromTheAPI["author"]

Does it work this way?`

So if I understand correctly, the init? Method is simply setting up an instance of Book to accept the "value" from a dictionary. It uses the guard statement to ensure that both "title" and "book" are present, otherwise it returns nil.

Perfect?

So to return the keys, I should be creating a function that returns the appropriate key for each value of the dictionary that is input?

I don't understand that. Can you give me more details?

Ahhh, I think that now I got what you mean..

"But the initialiser accepts [String : String]. I don't understand how this works."

[String: String] in Swift is a Dictionary. So the init is right when it asks you a dictionary. You have to pass a dictionary where the keys are String and the values are String as well.

Like this one here.

var dict = [String : String]()
dict["title"] = "title" 
dict["author"] = "author"

var book = Book(dict: dict)

Yes I understand that the init method is asking for a dictionary

But how would I obtain the values in the dictionary, using only the keys? The init method asks for both a value and a key?

And you create a dictionary, then you somehow assign it only 1 string

dict["author"]

How does this work? Isn't a dictionary like this [String : String]?