@dynamicMemberLookup public struct Tagged<Tag, RawValue> {
  public var rawValue: RawValue
  public init(rawValue: RawValue) {
    self.rawValue = rawValue
  }
  public subscript<Subject>(dynamicMember keyPath: KeyPath<RawValue, Subject>) -> Subject {
    rawValue[keyPath: keyPath]
  }
}

extension Tagged: Hashable, Equatable where RawValue: Hashable {
  public func hash(into hasher: inout Hasher) {
    hasher.combine(self.rawValue)
  }
}

func testHashable() {
  enum Tag { }
  Tagged<Tag, Int>(rawValue: 1).hashValue //ambiguous reference to member hashValue
}