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How to list all cases in an enum using CaseIterable

Paul Hudson       @twostraws

Swift 4.2 introduced a new CaseIterable protocol that automatically generates an array property of all cases in an enum. To enable it, all you need to do is make your enum conform to the CaseIterable protocol and at compile time Swift will automatically generate an allCases property that is an array of all your enum’s cases, in the order you defined them.

For example, this creates an enum of colors and asks Swift to automatically generate an allCases array for it:

enum Color: CaseIterable {
    case red, green, blue
}

You can then use that property as a regular array – it will be a [Color] given the code above, so we could print each case like this:

for color in Color.allCases {
    print("My favorite color is \(color).")
}

This automatic synthesis of allCases will only take place for enums that do not have associated values. Adding those automatically wouldn’t make sense, however if you want you can add it yourself:

enum Car: CaseIterable {
    static var allCases: [Car] {
        return [.ford, .toyota, .jaguar, .bmw, .porsche(convertible: false), .porsche(convertible: true)]
    }

    case ford, toyota, jaguar, bmw
    case porsche(convertible: Bool)
}

Swift can’t synthesize an allCases property if any enum cases are marked unavailable. So, if you need allCases then you’ll need to add it yourself, like this:

enum Direction: CaseIterable {
    static var allCases: [Direction] {
        return [.north, .south, .east, .west]
    }

    case north, south, east, west

    @available(*, unavailable)
    case all
}

Note: You must add CaseIterable to the original declaration of your enum rather than an extension in order for the allCases array to be synthesized – you can’t use extensions to retroactively make existing enums conform to the protocol.

Available from iOS 8.0

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