typealias PartialKeyPathSet<Root> = Set<PartialKeyPath<Root>>

protocol _Drivable: AnyObject {}

extension _Drivable {
  typealias Driver = GenericDriver<Self>
  var driver: GenericDriver<Self> {
    get { return GenericDriver<Self>(driving: self) }
    set { /* no-op to allow mutation */ }
  }
}

struct GenericDriver<Drivable> {
  let __drivable: Drivable
  init(driving drivable: Drivable) {
    self.__drivable = drivable
  }
}

protocol Configurator {
  associatedtype Drivable: _Drivable
  typealias Driver = Drivable.Driver
  typealias DriverKeyPathSet = PartialKeyPathSet<Driver>
  func configure(_ driver: inout Driver, using set: DriverKeyPathSet)
}

struct AnyConfigurator<Drivable: _Drivable>: Configurator {
  private let _base: Any
  private let _function: (inout Driver, DriverKeyPathSet) -> Void

  init<Other>(_ other: Other)
    where
    Other: Configurator,
    Other.Drivable == Drivable
  {
    _base = other
    _function = other.configure(_:using:)
  }

  // error: Reference to invalid type alias 'Driver' of type 'AnyConfigurator<Drivable>'
  func configure(_ driver: inout Driver, using set: DriverKeyPathSet) {
    _function(&driver, set)
  }
}