如何在 Swift 中枚举 OptionSetType？

我在 Swift 中有一个自定义的 OptionSetType 结构。如何枚举一个实例的所有值？

这是我的选项集类型：

struct WeekdaySet: OptionSetType {
    let rawValue: UInt8

    init(rawValue: UInt8) {
        self.rawValue = rawValue
    }

    static let Sunday        = WeekdaySet(rawValue: 1 << 0)
    static let Monday        = WeekdaySet(rawValue: 1 << 1)
    static let Tuesday       = WeekdaySet(rawValue: 1 << 2)
    static let Wednesday     = WeekdaySet(rawValue: 1 << 3)
    static let Thursday      = WeekdaySet(rawValue: 1 << 4)
    static let Friday        = WeekdaySet(rawValue: 1 << 5)
    static let Saturday      = WeekdaySet(rawValue: 1 << 6)
}

我想要这样的事情：

let weekdays: WeekdaySet = [.Monday, .Tuesday]
for weekday in weekdays {
    // Do something with weekday
}

从 Swift 4 开始，标准库中没有方法 枚举一个元素OptionSetType（斯威夫特2）分别。OptionSet（斯威夫特 3、4）。

这是一个可能的实现，它只检查每个位 基础原始值，并且对于设置的每个位， 返回相应的元素。 “溢出乘法”&* 2用作左移，因为<<只为具体的整数类型定义，但不为IntegerType协议。

斯威夫特 2.2：

public extension OptionSetType where RawValue : IntegerType {

    func elements() -> AnySequence<Self> {
        var remainingBits = self.rawValue
        var bitMask: RawValue = 1
        return AnySequence {
            return AnyGenerator {
                while remainingBits != 0 {
                    defer { bitMask = bitMask &* 2 }
                    if remainingBits & bitMask != 0 {
                        remainingBits = remainingBits & ~bitMask
                        return Self(rawValue: bitMask)
                    }
                }
                return nil
            }
        }
    }
}

用法示例：

let weekdays: WeekdaySet = [.Monday, .Tuesday]
for weekday in weekdays.elements() {
    print(weekday)
}

// Output:
// WeekdaySet(rawValue: 2)
// WeekdaySet(rawValue: 4)

Swift 3:

public extension OptionSet where RawValue : Integer {

    func elements() -> AnySequence<Self> {
        var remainingBits = rawValue
        var bitMask: RawValue = 1
        return AnySequence {
            return AnyIterator {
                while remainingBits != 0 {
                    defer { bitMask = bitMask &* 2 }
                    if remainingBits & bitMask != 0 {
                        remainingBits = remainingBits & ~bitMask
                        return Self(rawValue: bitMask)
                    }
                }
                return nil
            }
        }
    }
}

Swift 4:

public extension OptionSet where RawValue: FixedWidthInteger {

    func elements() -> AnySequence<Self> {
        var remainingBits = rawValue
        var bitMask: RawValue = 1
        return AnySequence {
            return AnyIterator {
                while remainingBits != 0 {
                    defer { bitMask = bitMask &* 2 }
                    if remainingBits & bitMask != 0 {
                        remainingBits = remainingBits & ~bitMask
                        return Self(rawValue: bitMask)
                    }
                }
                return nil
            }
        }
    }
}