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Swift Case Iterable

An enum that adopts CaseIterable gains a list of all its cases. That list is called allCases.

Counting the cases

The Compass enum adopts CaseIterable beside its String raw type. The count of allCases matches the four written cases.

enum Compass: String, CaseIterable {
    case north
    case south
    case east
    case west
}
print(Compass.allCases.count)

Mapping the cases to raw values

The map call turns each case in allCases into its raw value. The printed array keeps the declaration order of the cases.

enum Compass: String, CaseIterable {
    case north
    case south
    case east
    case west
}
let names = Compass.allCases.map { $0.rawValue }
print(names)

Looping over every case

The loop walks allCases from the first case to the last case. Each pass prints the raw value of one case.

enum Compass: String, CaseIterable {
    case north
    case south
    case east
    case west
}
for direction in Compass.allCases {
    print(direction.rawValue)
}

Reading one case by position

allCases is a collection, so square brackets read one case by its position. Position 0 holds the first declared case.

enum Size: CaseIterable {
    case small
    case medium
    case large
}
print(Size.allCases[0])
print(Size.allCases.count)

Example

enum Season: String, CaseIterable {
    case spring
    case summer
    case autumn
    case winter
}
print(Season.allCases.count)
print(Season.allCases.map { $0.rawValue })

Key points

  • Adopting CaseIterable adds an allCases collection to the enum.
  • allCases holds one value for each case the enum declares.
  • The cases sit in allCases in declaration order.
  • allCases.count gives how many cases the enum declares.
  • A loop can walk allCases like any other collection.

In this example, the Season enum adopts CaseIterable and lists four cases. The first print shows the count of allCases, which is 4. The second print maps each case to its raw value and shows the four names in declaration order.

Note

An enum whose cases carry associated values cannot adopt CaseIterable.

Try it Yourself

Edit the code, then press Run.

Running is simulated

Exercise

In which order do the cases appear in allCases?