protocol AnyC {
  func foo()
}

protocol AnyEvent {}

protocol A {
  associatedtype C: AnyC
}

protocol EventA: A {
  associatedtype Event
}

typealias Container<Namespace>
  = (event: Namespace.Event, c: Namespace.C) where Namespace: EventA

enum ConcreteA: EventA {
  struct C: AnyC {
    func foo() {
      print("ConcreteA")
    }
  }

  enum Event: AnyEvent {
    case test
  }
}

func coordinate(_ event: AnyEvent, from c: AnyC) {
  switch (event, c) {
  // warning: Cast from '(AnyEvent, AnyC)' to unrelated type 'Container<ConcreteA>' (aka '(event: ConcreteA.Event, c: ConcreteA.C)') always fails
  case let container as Container<ConcreteA>:
    container.c.foo()
  default:
    print("default")
  }
}

let event: AnyEvent = ConcreteA.Event.test
let c: AnyC = ConcreteA.C()

coordinate(event, from: c)