Associated values in Swift

Enum cases carry payloads; switch unpacks them.

// Enum cases can carry payloads; switch unpacks them.
enum RaceSignal {
    case shorten(atMark: String)
    case recall(sailNumbers: [Int])
}

func announce(_ signal: RaceSignal) -> String {
    switch signal {
    case .shorten(let mark):
        return "Finish shortened at \(mark)"
    case .recall(let numbers) where numbers.count > 2:
        return "General recall"
    case .recall(let numbers):
        return "Individual recall: \(numbers)"
    }
}

print(announce(.shorten(atMark: "leeward")))
print(announce(.recall(sailNumbers: [207, 88])))
print(announce(.recall(sailNumbers: [207, 88, 415])))

How it works

1. case shorten(atMark: String) stores data in the case.
2. case .recall(let numbers) where ... binds and guards.
3. Case order matters: the guarded arm is tried first.

Keywords and builtins used here

• Int
• RaceSignal
• String
• announce
• case
• count
• enum
• func
• let
• print
• return
• switch
• where

The run, in numbers

Lines

20

Characters to type

556

Tokens

137

Three-star pace

65 tpm

At the three-star pace of 65 tokens a minute, this run takes about 126 seconds.

Type this snippet

Step 2 of 3 in Abstractions, step 20 of 27 in Language basics.

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