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CaseIterableにindexプロパティを追加する

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CaseIterableを拡張し、indexプロパティを追加する実装です。

実装コード

extension CaseIterable where Self: Equatable {
    var index: Int {
        guard let index = Self.allCases.firstIndex(of: self) as? Int else { fatalError() }
        return index
    }
}

利用例

enum Season: CaseIterable {
    case spring
    case summer
    case fall
    case winter
}

let season: Season = .fall
print(season.index) // 2
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