func exampleFunc() async {
  let isNotSendable = MyClass()

  // Value of non-Sendable type ... accessed after being transferred; 
  // later accesses could race
  Task {
    isNotSendable.count += 1
  }

  // Access can happen concurrently
  print(isNotSendable.count)
}

struct SingleUseTicket: ~Copyable {
    let ticketID: Int
    
    consuming func invalidate() {
        print("Ticket \(ticketID) invalidated.")
        
        // cleanup logic
        
        discard self
    }
    
    deinit {
        print("Ticket deinitialized.")
        
        // cleanup logic
    }
}

func testFibonacciSequenceThrowsError() async throws {
    do {
        let _ = try await fibonacciSequence(count: -1)
        XCTFail("Expected an error for negative count, but no error was thrown")
    } catch FibonacciError.invalidCount {
        // Success! The expected error was thrown.
    } catch {
        XCTFail("Unexpected error thrown: \(error)")
    }
}