This demonstrates that Shared in TCA will automatically add observability to value types such as structs, but not to reference types such as classes.

SharedObservable

//
//  SharedObservable.swift
//  SpeechExample
//
//  Created by Daniel Lyons on 2024-04-01.
//

import ComposableArchitecture
import Foundation
import SwiftUI
import Observation

// This demonstrates that Shared will automatically add observability to value
// types such as structs, but not to reference types such as classes.

@Observable class ObservableClassModel {
  var count = 0
}

class NonObservableClassModel {
  var count = 0
}


struct StructModel {
  var count = 0
}

@Reducer struct SharedObservableReducer {
  @ObservableState struct State {
    @Shared var structModel: StructModel // observable for free
    @Shared var observableClassModel: ObservableClassModel
    @Shared var nonObservableClassModel: NonObservableClassModel
  }
  enum Action {
    case incrementAll, decrementAll
    case incrementNonObservableClass, decrementNonObservableClass
  }
  
  var body: some ReducerOf<Self> {
    Reduce { state, action in
      switch action {
        case .incrementAll:
          state.structModel.count += 1
          state.observableClassModel.count += 1
          state.nonObservableClassModel.count += 1
          return .none
          
        case .decrementAll:
          state.structModel.count -= 1
          state.observableClassModel.count -= 1
          state.nonObservableClassModel.count -= 1
          return .none
          
        case .incrementNonObservableClass:
          state.nonObservableClassModel.count += 1
          return .none
          
        case .decrementNonObservableClass:
          state.nonObservableClassModel.count -= 1
          return .none
      }
    }
  }
  
}

struct SharedObservableView: View {
  let store: StoreOf<SharedObservableReducer> = .init(
    initialState: SharedObservableReducer.State(
      structModel: Shared(StructModel()),
      observableClassModel: Shared(ObservableClassModel()),
      nonObservableClassModel: Shared(NonObservableClassModel())
    )
  ) {
      SharedObservableReducer()
    }
  
  var body: some View {
    LabeledContent("StructModel Count", value: store.structModel.count.formatted(.number))
    LabeledContent("ObservableClassModel Count", value: store.observableClassModel.count.formatted(.number))
    LabeledContent("NonObservableClassModel Count", value: store.nonObservableClassModel.count.formatted(.number))
    Button("Increment All") { store.send(.incrementAll) }
    Button("Decrement All") { store.send(.decrementAll) }
    Button("Increment NonObservableClassModel") { store.send(.incrementNonObservableClass )}
    Button("Decrement NonObservableClassModel") { store.send(.decrementNonObservableClass )}
  }
}

#Preview {
  SharedObservableView()
}