swift - 嵌套枚举以允许多个时间范围

Question

我希望实现某种风格的枚举语法/功能，但我不确定如何实现它。目前我有以下内容:

internal enum Timeframe: Equatable {

    // MARK: - Cases

    case hour(count: Int)
    case day(count: Int)
    case week(count: Int)
    case month(count: Int)
    case year(count: Int)
    case all
    case exact(date: Date)
    case unspecified
}

除非需要，否则我想消除计数关联值。例如:

let oneDayTimeframe: Timeframe = .day
let twoDayTimeframe: Timeframe = .day.multiplied(by: 2)

这可能吗？即使没有办法完全实现我正在寻找的东西，我也会很感激有关潜在改进的建议。在大多数情况下，我最终使用 (count: 1)，这看起来有点冗长。如果默认值与关联值一起可用，我会使用

case hour(count: Int = 1)

有什么建议吗？

Answer 1

对您提供的答案进行一些迭代:

enum TimeFrame: Equatable {

    case all
    case countable(timeFrame: CountableTimeFrame)
    case exact(date: Date)
}

enum CountableTimeFrame: Equatable {

    case hour
    case day
    case week
    case month
    case year

    indirect case multiple(CountableTimeFrame, Int)

    var timeFrame: TimeFrame {
        return .countable(timeFrame: self)
    }

    static func * (left: CountableTimeFrame, right: Int) -> CountableTimeFrame {
        switch left {
        case .multiple(let timeFrame, let count):
            return .multiple(timeFrame, count * right)
        default:
            return .multiple(left, right)
        }
    }

    static func * (left: Int, right: CountableTimeFrame) -> CountableTimeFrame {
        return right * left
    }
}

将禁止滥用，例如不允许:

let timeFrame: TimeFrame = .multiple(.exact(date: someDate), 666)
let timeFrame: TimeFrame = .multiple(unspecified, 40)
let timeFrame: TimeFrame = .multiple(all, -1) 

并允许使用 * 运算符进行乘法运算，例如

let timeFrame: CountableTimeFrame = 4 * .hour
print(timeFrame) // multiple(__lldb_expr_5.CountableTimeFrame.hour, 4)
print(timeFrame * 2) // multiple(__lldb_expr_5.CountableTimeFrame.hour, 8)

和.unspecified:

let optionalTimeFrame: TimeFrame? = nil