Simplest MVVM with Combine

App.swift

import Foundation
import SwiftUI
import Combine

struct API {
  //private let url = URL(string: "https://hacker-news.firebaseio.com/v0/newstories.json")!
  private let url = URL(string: "https://hacker-news.firebaseio.com/wrongendpoint")!
  enum Error: LocalizedError, Identifiable {
    var id: String { localizedDescription }
    case addressUnreachable(URL)
    case invalidResponse
    var errorDescription: String? {
      switch self {
        case .invalidResponse:
          return "The server responded with garbage 🗑"
        case .addressUnreachable(let url):
          return "\(url) is unreachable"
      }
    }
    
  }
  func request() -> AnyPublisher<[Int], API.Error> {
    URLSession.shared.dataTaskPublisher(for: url)
      .receive(on: DispatchQueue.main)
      .map { $0.data }
      .decode(type: [Int].self, decoder: JSONDecoder())
      .mapError { error in
        switch error {
          case is URLError:
            return Error.addressUnreachable(url)
          default:
            return Error.invalidResponse
        }
      }
      .eraseToAnyPublisher()
  }
}

class ViewModel: ObservableObject {
  private let api = API()
  private var subscriptions = Set<AnyCancellable>()
  @Published var ids: [Int] = []
  @Published var error: API.Error? = nil
  func fetch() {
    api.request()
      .sink(receiveCompletion: { completion in
            switch completion {
              case .finished: print("finsihed")
              case .failure(let error):
                self.error = error
                return print("🤮 \(error.localizedDescription)")
            }
          },
            receiveValue: { ids in
              self.ids = ids
            })
      .store(in: &subscriptions)
  }
}

@main
struct MVVMApp: App {
  private let model = ViewModel()
  var body: some Scene {
    WindowGroup {
      ContentView(model: model)
        .onAppear {
          model.fetch()
        }
    }
  }
}

struct ContentView: View {
    @ObservedObject var model: ViewModel
    var body: some View {
      List(model.ids, id:\.self){ id in
        Text("Story id")
        Text(String(id)).padding()
      }
      .alert(item: self.$model.error) { error in
          Alert(title: Text("🤮 Network Error"),
              message: Text(error.localizedDescription),
              dismissButton: .cancel())
      }
    }
}

Show Network Error alert.