Can someone explain the following code?

Question

I understand that the code is intializing the Contacts struct. However I need clarification on what's going on inside the init? method, more specificaly the use of the subscripts with the parameter "dictionary."

struct Contact {
    let firstName: String
    let lastName: String
    let phone: String
    let email: String
    let street: String
    let city: String
    let state: String
    let zip: String
    let image: UIImage?
    var isFavorite: Bool
}

extension Contact {

    struct Key {
        static let firstName = "firstName"
        static let lastName = "lastName"
        static let phone = "phoneNumber"
        static let email = "email"
        static let street = "streetAddress"
        static let city = "city"
        static let state = "state"
        static let zip = "zip"
        static let image = "avatarName"
    }

//this is where I am stuck...
    init?(dictionary: [String: String]) {
        guard let firstNameString = dictionary[Key.firstName],
            let lastNameString = dictionary[Key.lastName],
            let phoneString = dictionary[Key.phone],
            let emailString = dictionary[Key.email],
            let streetString = dictionary[Key.street],
            let cityString = dictionary[Key.city],
            let stateString = dictionary[Key.state],
            let zipString = dictionary[Key.zip] else { return nil }

        self.firstName = firstNameString
        self.lastName = lastNameString
        self.phone = phoneString
        self.email = emailString
        self.street = streetString
        self.city = cityString
        self.state = stateString
        self.zip = zipString

        if let imageName = dictionary[Key.image] {
            self.image = UIImage(named: imageName)
        } else {
            image = nil
        }

        isFavorite = false
    }
}

Answer 1 · 2018-01-24T04:56:02Z

January 24, 2018 4:56am

Hello,

It's simple really, the init is a fail-able initializer, that takes a dictionary as its parameter. So inside of it, you have a guard that if any of the information is missing, it will fail to initialize the struct.

// We have a dictionary
let someCarDictionary: [String : String] = ["fiesta" : "Ford Fiesta" , "mustang" : "Ford Mustang"]

// This is how we retrieve a value from a dictionary, by passing it the key. ( Key Value )
let car = someCarDictionary["fiesta"] 
print(car) // Will print "Ford Fiesta"

So in the init, all it's doing is passing keys for the respective value to be able to initialize all its properties.

Hope that helps you a bit.

If you need a more detail answer let me know.

Good luck

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Peter Correa

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Can someone explain the following code?

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Jhoan Arango

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Peter Correa

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