Enums

Without Associated Type

• Creation :

  enum CompassPoint {
      case north
      case south
      case east
      case west
  }
  

  enum Planet {
      case mercury, venus, earth, mars, jupiter, saturn, uranus, neptune
  }
  

• Access :

  var directionToHead = CompassPoint.west
  

  • Once directionToHead  is declared as a CompassPoint , you can set it to a different CompassPoint  value using a shorter dot syntax:

    directionToHead = .east
    

    directionToHead = .south
    switch directionToHead {
    case .north:
        print("Lots of planets have a north")
    case .south:
        print("Watch out for penguins")
    case .east:
        print("Where the sun rises")
    case .west:
        print("Where the skies are blue")
    }
    

With Associated Type

• Creation :

  enum Barcode {
      case upc(Int, Int, Int, Int)
      case qrCode(String)
  }
  

  • This definition doesn’t provide any actual Int  or String  values — it just defines the type  of associated values that constants and variables can store when they’re equal to Barcode.upc  or Barcode.qrCode .

  var productBarcode = Barcode.upc(8, 85909, 51226, 3)
  
  productBarcode = .qrCode("ABCDEFGHIJKLMNOP")
  

• Access :

  switch productBarcode {
  case .upc(let numberSystem, let manufacturer, let product, let check):
      print("UPC: \(numberSystem), \(manufacturer), \(product), \(check).")
  case .qrCode(let productCode):
      print("QR code: \(productCode).")
  }
  // Prints "QR code: ABCDEFGHIJKLMNOP."
  

  • If all of the associated values for an enumeration case are extracted as constants, or if all are extracted as variables, you can place a single let  or var  annotation before the case name, for brevity:

    switch productBarcode {
    case let .upc(numberSystem, manufacturer, product, check):
        print("UPC : \(numberSystem), \(manufacturer), \(product), \(check).")
    case let .qrCode(productCode):
        print("QR code: \(productCode).")
    }
    // Prints "QR code: ABCDEFGHIJKLMNOP."
    

Iterating

• Swift exposes a collection of all the cases as an allCases  property of the enumeration type if you write CaseIterable  after the enumeration’s name.

enum Beverage: CaseIterable {
    case coffee, tea, juice
}

let numberOfChoices = Beverage.allCases.count
print("\(numberOfChoices) beverages available")
// Prints "3 beverages available"


for beverage in Beverage.allCases {
    print(beverage)
}
// coffee
// tea
// juice

Default Value

• Swift enumeration cases don’t have an integer value set by default.

• In the CompassPoint  example above, north , south , east  and west  don’t implicitly equal 0 , 1 , 2  and 3 . Instead, the different enumeration cases are values in their own right, with an explicitly defined type of CompassPoint .

Other Topics

• Raw Values.

• Recursive Enumerations.