Enum & Optionals

Question 1

What’s the purpose of using an enum?

Answer 1

An enum is great to use for a group of related values that defines a common type.

So let’s say we wanted to do something related to days of the week, Day is the common type with the different days serving as values or cases

enum Day {
    case monday
    case tuesday
    case wednesday
    case thursday
    case friday
    case saturday
    case sunday
}

Question 2

Can you incorporate a function into an enum?

Answer 2

Yes.

enum ColorComponent {
    case rgb(Float, Float, Float, Float)
    case hsb(CGFloat, CGFloat, CGFloat, CGFloat)

    func color() -> UIColor {
        switch self {
        case .rgb(let red, let green, let blue, let alpha):
            return UIColor(colorLiteralRed: red/255.0, green: green/255.0, blue: blue/255.0, alpha: alpha)
        case .hsb(let hue, let saturation, let brightness, let alpha):
            return UIColor(hue: hue/360.0, saturation: saturation/100.0, brightness: brightness/100.0, alpha: alpha)
        }
    }
}

ColorComponent.rgb(230.0, 26.0, 193.0, 1).color()

Question 3

What’s the purpose of using optionals?

Answer 3

It’s a great way for us to know that the specific item may or may not have a value. Such as:

struct Friend {
    var firstName: String
    var middleName: String?
    var lastName: String
  }

Not everyone has a middle name!

Question 4

What is the purpose of using a guard statement?

Answer 4

An early exit or guard statement is a way of checking for success cases first. You deal with errors up front and exit the scope.

You use them for non optional values?

guard let name = friendDictionary["name"], let age = friendDictionary["age"] else {
        return nil
    }

Question 5

Why would you want to create an enum with default raw values?

Answer 5

Those cases may have values that are not going to change. Such as:

enum Coin: Double {
    case penny = 0.01
    case nickel = 0.05
    case dime = 0.10
    case quarter = 0.25
}

Question 6

When we create an optional value in a class, it is automatically initialized to what? Example var buildingName: String?

Answer 6

Nil

Question 7

What is the rawValue of the third item of an emun with type Int?

Answer 7

3

Question 8

What is the rawValue of the fourth item of enum with type String that is called post?

Answer 8

“Post”

Question 9

What is the syntax for a failable initializer?

Answer 9

Init?
init?(dictionary: [String: String]) {
return nil
}

Question 10

What is the purpose of optional chaining?

Answer 10

It helps us get the value of something without doing a bunch of if lets to check if the value might be nil 
let buildingNumber = susan.residence?.address?.buildingNumber

Question 11

Do you need an initializer for classes with stored properties set up as optional variables or default types?

Answer 11

No you do not. It is automatically initialized as nil

See Classes Address, Residence , Person

Question 12

TF: only an optional type can be set to nil

Answer 12

True

Question 13

When an enum member has an associated value, how do you access it?

Answer 13

By binding it to a local constant

See the colorComponent enum example

Question 14

TF: Raw value initializers accept any value that conforms to the type requirements. An optional value allows the initializer to return nil in case there is no match.

Answer 14

True

Question 15

When an enum has a default value for a case, what is that value called? i.e. case tab = “/t”

Answer 15

A raw value

Question 16

When an enum has a value type, what is that value called? I.e. case qrCode(String)

Answer 16

An associated value

Question 17

What is the nil-coalescing operator?

Answer 17

a ?? b

This unwraps the optional a if it has a value or returns a default value of b if a is nil

Question 18

TF: You cannot include a control transfer statement in the else clause of a guard statement

Answer 18

False

Question 19

TF: Enums are well suited for use with switch statements because the compiler can deduce exhaustiveness

Answer 19

True

Question 20

TF: Associated values allow us to provide default values to our enumeration members

Answer 20

False

Question 21

What is the value of `c` given the code below? 
var a: Int? = nil
let b = 2

let c = a ?? b

Answer 21

2

Question 22

TF: Enums can do everything structs and classes can do including contain stored properties

Answer 22

False

Question 23

TF: In an optional chaining expression, if one part of the expression fails, an error is raised

Answer 23

False