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[Swift] CaseIterableなEnumの次の要素を取得する

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動機

N-State toggle buttonが欲しかった。

経緯

N個の状態を渡すと、ボタンを押すたびに順に状態が変わるボタン。
例えば ["State1", "State2", "State3", "State4"]を渡すと、クリックするたびにそのラベルが State1 → State2 → State3 → State4 → State1 → と変わっていくボタン。

Swiftなのだから、状態はenumで持ちたい。

そうなると、ローテーションができないのでは????

CaseIterableを使えばいけるかも。

結果

できた!

extension CaseIterable where Self: Equatable {

    func next() -> Self {

      let all = Array(Self.allCases)
      let count = all.count

      return all.firstIndex(of: self).map { all[($0 + 1) % count] }!
    }
}

問題点

あれ?
CaseIterable#allCasesの順番がどうなるかが不定...

masakihori
非えんじにあ / 素人が雰囲気で書いてます
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