Enumerations
Defining an Enumeration
Enumerations (or enums) are used to define a new custom type with a list of possible cases. When creating an instance of an enumeration, its value must be one of the cases.
enum Day {case mondaycase tuesdaycase wednesdaycase thursdaycase fridaycase saturdaycase sunday}let casualWorkday: Day = .friday
Switch Statements
Switch statements are used to determine the case of an enumeration. When switching on an enumeration, all cases must be addressed if a default is not provided. Switching on enumerations can also access the associated values of a case.
enum Dessert {case cake(flavor: String)case vanillaIceCream(scoops: Int)case brownie}let customerOrder: Dessert = .cake(flavor: "Red Velvet")switch customerOrder {case let .cake(flavor):print("You ordered a \(flavor) cake")case let .vanillaIceCream(scoopCount):print("You ordered \(scoopCount) scoops of vanilla ice cream")case .brownie:print("You ordered a brownie")}// Prints: "You ordered a Red Velvet cake"
CaseIterable
Add conformance to the CaseIterable protocol to access an allCases property that returns an array of all the cases of an enumeration.
enum Season: CaseIterable {case wintercase springcase summercase fall}for season in Season.allCases {print(season)}
Raw Values
Enumerations can have a raw value associated with each case by adding : RawValueType after the enumeration name. A String, Character, Int, Double, or Float can be assigned as a raw value. Enumerations with a raw value can be instantiated using the init(rawValue:). Instances of enumerations with a raw value have a rawValue property.
enum Grade: Character {case pass = "P"case fail = "F"}let mathTest = Grade.passprint(mathTest.rawValue) // Prints "P"
Associated Values
Each case in an enumeration can have a value associated with it. Enumerations can have a raw value or cases with associated values, but not both.
enum Dessert {case cake(flavor: String)case vanillaIceCream(scoops: Int)case brownie}let customerOrder: Dessert = .cake(flavor: "Red Velvet")
Instance Methods
Just like classes and structures, enumerations can have instance methods. If an instance method changes the value of the enumeration, it needs to be marked as mutating.
enum Traffic {case lightcase mediumcase heavymutating func reportAccident() {self = .heavy}}var currentTraffic: Traffic = .lightcurrentTraffic.reportAccident() // currentTraffic is now .heavy
Computed Properties
An enumeration can have computed properties defined within its declaration. Enumerations cannot contain stored properties.
enum ShirtSize: String {case small = "S"case medium = "M"case large = "L"case extraLarge = "XL"var description: String {return "This shirt size is \(self.rawValue)"}}
