OptionSetIterator.swift

public struct OptionSetIterator<Element: OptionSet>: IteratorProtocol where Element.RawValue == Int {
  private let value: Element

  init(element: Element) {
    self.value = element
  }

  private lazy var remainingBits = value.rawValue
  private var bitMask = 1

  public mutating func next() -> Element? {
    while remainingBits != 0 {
      defer { bitMask = bitMask &* 2 }
      if remainingBits & bitMask != 0 {
        remainingBits = remainingBits & ~bitMask
        return Element(rawValue: bitMask)
      }
    }
    return nil
  }
}

extension OptionSet where Self.RawValue == Int {
  public func makeIterator() -> OptionSetIterator<Self> {
    OptionSetIterator(element: self)
  }
}