Async / Await in Swift

Combine Version.swift

func loadWebResource(_ path: String) -> AnyPublisher<Resource, Error>
func decodeImage(_ r1: Resource, _ r2: Resource) -> AnyPublisher<Image, Error>
func dewarpAndCleanupImage(_ i : Image) -> AnyPublisher<Image, Error>

func processImageData1() -> AnyPublisher<Image, Error> {
  loadWebResource("dataprofile.txt").zip(loadWebResource("imagedata.txt")).flatMap { (dataResource, imageResource) in
    decodeImage(dataResource, imageResource)
  }
  .flatMap { imageTmp in 
    dewarpAndCleanup(imageTmp)
  }
  .eraseToAnyPublisher()
}

Future Wrapper.swift

func loadWebResource(filename: String) -> AnyPublisher<Data, Error> {
  URLSession.shared.dataTask(with: URL(string: BASE_URL + filename)!) { data, response, error in 
    guard error == nil else {
      promise(.failure(error!))
    }
    
    promise(.success(data))
  }.eraseToAnyPublisher()
}

Manifesto Callback Example.swift

// from https://gist.github.com/lattner/31ed37682ef1576b16bca1432ea9f782

func processImageData2(completionBlock: (result: Image?, error: Error?) -> Void) {
    loadWebResource("dataprofile.txt") { dataResource, error in
        guard let dataResource = dataResource else {
            completionBlock(nil, error)
            return
        }
        loadWebResource("imagedata.dat") { imageResource, error in
            guard let imageResource = imageResource else {
                completionBlock(nil, error)
                return
            }
            decodeImage(dataResource, imageResource) { imageTmp, error in
                guard let imageTmp = imageTmp else {
                    completionBlock(nil, error)
                    return
                }
                dewarpAndCleanupImage(imageTmp) { imageResult in
                    guard let imageResult = imageResult else {
                        completionBlock(nil, error)
                        return
                    }
                    completionBlock(imageResult)
                }
            }
        }
    }
}

Manifesto Fixed.swift

// from https://gist.github.com/lattner/31ed37682ef1576b16bca1432ea9f782

func loadWebResource(_ path: String) async -> Resource
func decodeImage(_ r1: Resource, _ r2: Resource) async -> Image
func dewarpAndCleanupImage(_ i : Image) async -> Image

func processImageData1() async -> Image {
    let dataResource  = await loadWebResource("dataprofile.txt")
    let imageResource = await loadWebResource("imagedata.dat")
    let imageTmp      = await decodeImage(dataResource, imageResource)
    let imageResult   = await dewarpAndCleanupImage(imageTmp)
    return imageResult
}

URL Session.swift

func loadWebResource(filename: String) -> AnyPublisher<Data, Error> {
    URLSession.shared.dataTaskPublisher(for: URL(string: BASE_URL + filename)!)
        .eraseToAnyPublisher()
}

func processImageData1() -> AnyPublisher<Image, Error> {
  loadWebResource("dataprofile.txt").zip(loadWebResource("imagedata.txt")).flatMap { (dataResource, imageResource) in
    decodeImage(dataResource, imageResource)
  }
  .flatMap { imageTmp in 
    dewarpAndCleanup(imageTmp)
  }
  .eraseToAnyPublisher()
}