app-todos.state.ts

@State<number[]>({
  name: 'todos',
  defaults: [1, 2, 3]
})
export class AppState {

  @Selector() public static mutableTodos(state: number[]): number[] {
    return state.reverse();
  }

  @Selector() public static immutableTodos(state: number[]): number[] {
    return [...state].reverse();
  }

}