Enumerations
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Enumeration Syntax
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enum SomeEnumeration {
// enumeration definition goes here
}
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enum CompassPoint {
case north
case south
case east
case west
}
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enum Planet {
case mercury, venus, earth, mars, jupiter, saturn, uranus, neptune
}
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var directionToHead = CompassPoint.west
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directionToHead = .east
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Matching Enumeration Values with a Switch Statement
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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")
}
// Prints "Watch out for penguins"
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let somePlanet = Planet.earth
switch somePlanet {
case .earth:
print("Mostly harmless")
default:
print("Not a safe place for humans")
}
// Prints "Mostly harmless"
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Iterating over Enumeration Cases
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enum Beverage: CaseIterable {
case coffee, tea, juice
}
let numberOfChoices = Beverage.allCases.count
print("\(numberOfChoices) beverages available")
// Prints "3 beverages available"
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for beverage in Beverage.allCases {
print(beverage)
}
// coffee
// tea
// juice
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Associated Values
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enum Barcode {
case upc(Int, Int, Int, Int)
case qrCode(String)
}
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var productBarcode = Barcode.upc(8, 85909, 51226, 3)
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productBarcode = .qrCode("ABCDEFGHIJKLMNOP")
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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."
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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."
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Raw Values
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enum ASCIIControlCharacter: Character {
case tab = "\t"
case lineFeed = "\n"
case carriageReturn = "\r"
}
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Implicitly Assigned Raw Values
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enum Planet: Int {
case mercury = 1, venus, earth, mars, jupiter, saturn, uranus, neptune
}
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enum CompassPoint: String {
case north, south, east, west
}
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let earthsOrder = Planet.earth.rawValue
// earthsOrder is 3
let sunsetDirection = CompassPoint.west.rawValue
// sunsetDirection is "west"
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Initializing from a Raw Value
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let possiblePlanet = Planet(rawValue: 7)
// possiblePlanet is of type Planet? and equals Planet.uranus
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let positionToFind = 11
if let somePlanet = Planet(rawValue: positionToFind) {
switch somePlanet {
case .earth:
print("Mostly harmless")
default:
print("Not a safe place for humans")
}
} else {
print("There isn't a planet at position \(positionToFind)")
}
// Prints "There isn't a planet at position 11"
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Recursive Enumerations
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enum ArithmeticExpression {
case number(Int)
indirect case addition(ArithmeticExpression, ArithmeticExpression)
indirect case multiplication(ArithmeticExpression, ArithmeticExpression)
}
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indirect enum ArithmeticExpression {
case number(Int)
case addition(ArithmeticExpression, ArithmeticExpression)
case multiplication(ArithmeticExpression, ArithmeticExpression)
}
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let five = ArithmeticExpression.number(5)
let four = ArithmeticExpression.number(4)
let sum = ArithmeticExpression.addition(five, four)
let product = ArithmeticExpression.multiplication(sum, ArithmeticExpression.number(2))
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func evaluate(_ expression: ArithmeticExpression) -> Int {
switch expression {
case let .number(value):
return value
case let .addition(left, right):
return evaluate(left) + evaluate(right)
case let .multiplication(left, right):
return evaluate(left) * evaluate(right)
}
}
print(evaluate(product))
// Prints "18"
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