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如何仅检查swift嵌套枚举是否与外部枚举相等?

swift

Chris · 技术社区 · 6 年前

我试图用嵌套的枚举来描述我的模型,这样就不可能出现非法状态,并在顶层提供分类。现在,我的(简化)代码是:

enum SportsEvent {

    enum RunningEvent {
        case sprint
        case marathon
    }

    enum ThrowingEvent {
        case hammer
        case javelin
        case discus
    }

    case running(event: RunningEvent)
    case throwing(event: ThrowingEvent)

    func isSameCategory(as other: SportsEvent) -> Bool {

        return false
    }
}

let sprint = SportsEvent.running(event: .sprint)
let javelin = SportsEvent.throwing(event: .javelin)
let hammer = SportsEvent.throwing(event: .hammer)

sprint.isSameCategory(as: javelin)      // False
hammer.isSameCategory(as: javelin)      // True

感觉应该是琐碎的 if case ... 一个通配符,但我不知道如何实现。我希望不需要一个巨大的开关声明,因为我的实际模型更复杂。

2 回复 | 直到 6 年前

Martin R 6 年前

我认为您需要一个switch语句,其中有一个复合大小写列出所有外部枚举的可能相同值组合, 加上默认情况:

func isSameCategory(as other: SportsEvent) -> Bool {
    switch (self, other) {
    case (.running, .running),
         (.throwing, .throwing):
        return true
    default:
        return false
    }
}

或(归属于@hamish):

func isSameCategory(as other: SportsEvent) -> Bool {
    switch (self, other) {
    case (.running, .running),
         (.throwing, .throwing):
        return true
    case (.running, _),
         (.throwing, _):
        return false
    }
}

它的优点是编译器可以检查所有的情况。对于具有 n 使 2 * n switch语句中的事例(这比 n * n 如果你检查了所有可能的组合)。

Sulthan 6 年前

根据您的用例,您可能能够转换 SportEvent 协议:

enum RunningEvent {
    case sprint
    case marathon
}

enum ThrowingEvent {
    case hammer
    case javelin
    case discus
}

enum SportEventCategory {
    case running
    case throwing
}

protocol SportEvent {
    var category: SportEventCategory { get }
}

extension RunningEvent: SportEvent {
    var category: SportEventCategory {
        return .running
    }
}

extension ThrowingEvent: SportEvent {
    var category: SportEventCategory {
        return .throwing
    }
}

let sportEvent1: SportEvent = RunningEvent.sprint
let sportEvent2: SportEvent = ThrowingEvent.hammer
print(sportEvent1.category == sportEvent2.category)

甚至作为一个平面枚举:

enum SportEvent {
    enum Category {
        case running
        case throwing
    }

    case sprint
    case marathon
    case hammer
    case javelin
    case discus

    var category: Category {
        switch self {
        case .sprint, .marathon, .hammer:
            return .running
        case .javelin, .discus:
            return .throwing
        }
    }
}

let sportEvent1: SportEvent = .sprint
let sportEvent2: SportEvent = .marathon
print(sportEvent1.category == sportEvent2.category)

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