Some example of using observable object

Observe.swift

import SwiftUI
import Combine

final class ViewModel: ObservableObject {
  
  var subs: Set<AnyCancellable> = []
  
  // For some reason this does not work!
  
  init() {
    $message.filter { $0.count > 20 }
      .print()
      .map { String($0.prefix(20)) }
      .print()
      .assign(to: \.message, on: self)
      .store(in: &subs)
  }
  
  @Published var message = "Message"
}

struct ContentView: View {
  
  @ObservedObject var viewModel = ViewModel()
  
  var body: some View {
    VStack {
      Text(viewModel.message)
      TextField("", text: $viewModel.message)
        .textFieldStyle(RoundedBorderTextFieldStyle())
    }.padding()
  }
}