[Pitch] `@OptionSet` macro

Evolution Pitches
68

I don't understand your "explicit overrides", but

already works. But because of the need for manual forwarding, I don't think it's as good as my solution above.

To get rid of the manual forwarding, I don't think a special-case macro is a good idea. I understand people are excited to play with macros, but to improve OptionSet, they probably should be working on more generalized forwarding via static subscripts with dynamicMember instead.

struct ShippingOptions: OptionSet {
  private enum Option: BitFlag<RawValue> {
    case nextDay, secondDay
    // this bit is cursed, don't use it
    case priority = 3, standard
  }

  static let nextDay = Self(Option.nextDay)
  static let secondDay = Self(Option.secondDay)
  static let priority = Self(Option.priority)
  static let standard = Self(Option.standard)

  let rawValue: Int
}

public extension OptionSet {
  init(_ option: some RawRepresentable<some RawRepresentable<RawValue>>) {
    self.init(rawValue: option.rawValue.rawValue)
  }
}
BitFlag 
/// A representation of a single bit "flag".
public struct BitFlag<RawValue: BinaryInteger & _ExpressibleByBuiltinIntegerLiteral> {
  public let rawValue: RawValue

  public init?(rawValue: RawValue) {
    guard
      rawValue != 0,
      rawValue & (rawValue - 1) == 0
    else { return nil }

    self.rawValue = rawValue
  }
}

// MARK: - Equatable
extension BitFlag: Equatable { }

// MARK: - ExpressibleByIntegerLiteral
extension BitFlag: ExpressibleByIntegerLiteral {
  public init(integerLiteral flagIndex: RawValue) {
    self.init(rawValue: 1 << flagIndex)!
  }
}

// MARK: - RawRepresentable
extension BitFlag: RawRepresentable { }