在 Set 上使用 Switch 语句（Swift 3）答案

【问题标题】：Using Switch statements on Sets (Swift 3)在 Set 上使用 Switch 语句（Swift 3）
【发布时间】：2016-11-02 04:13:41
【问题描述】：

enum RepeatDay : String, CustomStringConvertible {
    case Monday = "Monday"
    case Tuesday = "Tuesday"
    case Wednesday = "Wednesday"
    case Thursday = "Thursday"
    case Friday = "Friday"
    case Saturday = "Saturday"
    case Sunday = "Sunday"

    var description : String { return rawValue }

    static let allValues = [Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday]
}

以上是在我的模型中声明的。这将是一个类似的用例，例如在设置闹钟时在股票时钟应用中选择日期。

但是下面的抱怨！！

            guard let repeatDay = $0 else { return "" }
            switch repeatDay {
            case .Monday :
                break
            default:
                break
            }

其中repeatDay 是一个集合，如上面的屏幕截图所示。

有没有办法在这种情况下使用 switch 语句？欢迎任何替代方案。

【问题讨论】：

给我们更多关于repeatDay声明的上下文
顺便说一句，当您的枚举具有 String 绘制值时，它的默认原始值设置为案例名称，因此您可以只写 case Monday 而不是 case Monday = "Monday"
哦，好的。但是，正如我所说的那样，我期望能够分别选择“星期一”、“星期二”和“工作日”，如果选择了所有五个工作日。
@AlexanderMomchliov，我想关于RepeatDay 没什么好解释的。我已经在上面的问题中发布了所有内容。
硬编码工作日的名称是个坏主意。 DateFormatter 具有多个属性，用于根据用户的区域设置获取完整和缩写的工作日名称。

标签： swift enums switch-statement

【解决方案1】：

试试这个

guard let repeatDay = RepeatDay(rawValue: $0) else { return "" }
    switch repeatDay {
    case .Monday :
        break
    default:
        break
    }

【讨论】：

【解决方案2】：

您正在打开Set<RepeatDay>，但案例是RepeatDay。 switch 语句无法知道您希望它如何处理这些不同的类型。

我怀疑您正在尝试匹配特定类型的天数集，例如工作日的天数集和周末的天数集。在这种情况下，您的 switch 的 case 语句需要为Set<RepeatDay，可以与提供的Set<RepeatDay> 进行比较。

switch days {
    case [.Monday, .Tuesday, .Wednesday, .Thursday, .Friday]:
        print("Weekdays")
    case [.Saturday, .Sunday]:
        print("Weekends")
    default:
        print(days)
}

我会将这些 case 语句的集合提取为 Day 枚举的静态成员，并添加更多逻辑来描述连续的天数间隔。您还可以从weekdaySymbols 的DateFormatter 获取天数的准确区域设置名称

import Foundation

extension Array where Element: Integer {
    func isConsecutive() -> Bool {
        guard var previous = self.first else { return true }

        for current in self[1 ..< self.count] {
            if current != previous + 1 { return false }
            previous = current
        }

        return true
    }
}

enum Day: Int, CustomStringConvertible {
    case Sunday
    case Monday
    case Tuesday
    case Wednesday
    case Thursday
    case Friday
    case Saturday

    /*TODO: Note that this stores the weekdaySymbols permanently once
    the app is launched. If there is a change in locale after the app
    launch, then the days will not be updated. If this is a concern,
    this `DayNames` constant should be deleted, and all references
    to it should be changed to DateFormatter().weekdaySymbols, which
    will dynamically obtain the weekdays accurate to the current locale */
    static let DayNames: [String] = DateFormatter().weekdaySymbols

    public var description: String { return Day.DayNames[self.rawValue] }

    static let Everyday: Set<Day> = [.Sunday, .Monday, .Tuesday, .Wednesday, .Thursday, .Friday, .Saturday]
    static let Weekdays: Set<Day> = [.Monday, .Tuesday, .Wednesday, .Thursday, .Friday]
    static let Weekends: Set<Day> = [.Saturday, .Sunday]



    static func describeDays(_ days: Set<Day>) -> String {
        guard days.count > 0 else { return "No days" }

        switch days { // Predefined cases
            case Day.Everyday: return "Everyday"
            case Day.Weekdays: return "Weekdays"
            case Day.Weekends: return "Weekends"
            default: break
        }

        let array = days.map{ $0.rawValue }.sorted()

        switch array {
            case _ where array.isConsecutive(): // Consecutive range of days
                let min = array.first!
                let max = array.last!
                return "\(Day(rawValue: min)!) - \(Day(rawValue: max)!)"
            default: return days.description //arbitrary days
        }
    }
}

print(Day.describeDays(Day.Everyday))
print(Day.describeDays(Day.Weekdays))
print(Day.describeDays(Day.Weekends))
print(Day.describeDays([.Monday, .Tuesday, .Wednesday, .Thursday])) // Monday - Thursday
print(Day.describeDays([.Tuesday, .Wednesday, .Thursday, .Saturday])) //[Saturday, Wednesday, Thursday, Tuesday]

You can see this in action, here.

【讨论】：

【解决方案3】：

你的闭包中$0的类型不是RepeatDay而是Set<RepeatDay>，试试这个：

guard let repeatDay = $0.first else { return "" }
    switch repeatDay {
    case .Monday :
        break
    default:
        break
    }

【讨论】：