Combine Example in Swift

CombineSample.swift

enum HTTPError: LocalizedError {
  case statusCode
}

enum RequestError: Error {
  case sessionError(error: Error)
}

struct Post: Codable {

    let id: Int
    let title: String
    let body: String
    let userId: Int
}

struct ToDo: Codable {
  
  let id: Int
  let title: String
  let completed: Bool
  let userId: Int
}

  var cancellable: AnyCancellable?

  func combineWithOutError() {
        
    let dummyURL = URL(string: "https://jsonplaceholder.typicode.com/posts")
    cancellable = URLSession.shared.dataTaskPublisher(for: dummyURL!)
    .map { $0.data }
    .decode(type: [Post].self, decoder: JSONDecoder())
    .replaceError(with: [])
    .eraseToAnyPublisher()
    .sink(receiveValue: { posts in
        print(posts.map { $0.id })
    })
  }
  
  func combineWithError() {
    
    let dummyURL = URL(string: "https://jsonplaceholder.typicode.com/posts")
    cancellable = URLSession.shared.dataTaskPublisher(for: dummyURL!)
    .tryMap { output in
      guard let response = output.response as? HTTPURLResponse, response.statusCode == 200 else {
        throw HTTPError.statusCode
      }
      print(response.statusCode)
      return output.data
    }
    .decode(type: [Post].self, decoder: JSONDecoder())
    .eraseToAnyPublisher()
    .sink(receiveCompletion: { completion in
        switch completion {
        case .finished:
            break
        case .failure(let error):
          print(error.localizedDescription)
        }
    }, receiveValue: { posts in
      print("Post Title\(posts.map({ $0.title }))")
    })
  }

  func combineMultipleRequest() {
    let url1 = URL(string: "https://jsonplaceholder.typicode.com/posts")!
    let url2 = URL(string: "https://jsonplaceholder.typicode.com/todos")!

    let postPublisher = URLSession.shared.dataTaskPublisher(for: url1)
      .map{ $0.data }
      .decode(type: [Post].self, decoder: JSONDecoder())

    let todoPublisher = URLSession.shared.dataTaskPublisher(for: url2)
      .map{ $0.data }
      .decode(type: [ToDo].self, decoder: JSONDecoder())

    cancellable = Publishers.Zip(postPublisher, todoPublisher)
    .eraseToAnyPublisher()
      .catch { _ in
          Just(([], []))
      }
    .sink(receiveValue: { posts, todos in
      print(posts.count)
      print(todos.count)
    })
  }