Converting a callback function to async await in Swift

Occasionally you will need to convert a callback based function to an async/await function. One example of this is below, calculating a map route appears to be only available as a callback based one. Below is an example of how to convert it to an async function. This code is actually used in Weather Driver.

func calculateSubRoute(route: MKRoute, step: MKRoute.Step) async throws -> MKDirections.Response? {
	return try await withCheckedThrowingContinuation { continuation in
		let request = MKDirections.Request()
		request.source = MKMapItem(placemark: MKPlacemark(coordinate: route.steps.first!.polyline.coordinate))
		request.destination = MKMapItem(placemark: MKPlacemark(coordinate: step.polyline.coordinate))
		request.requestsAlternateRoutes = true
		request.transportType = .automobile

		let directions = MKDirections(request: request)
		directions.calculate() { response, error in
			if error != nil {
				continuation.resume(throwing: error!)
			continuation.resume(returning: response)