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I am trying to use `ProvidableAmbient`  to pass data from screen1 to screen2. How  to update data in screen2 and return back to screen1 ?

I have tried to first pass to the data in screen2 but I am unable to update data. I tried using `provides()`  and `provides` to update the value but

`Providers` associates a value with an ambient only for children of the `Providers` composable. It doesn’t affect code above, before, or after itself. If `screen1` and `screen2` are siblings, how are you using ambients to communicate between them? The only way I could see that working is if a parent composable of both screens provided the same ambient value to both, and that value was some sort of mutable object (perhaps a `MutableState`) that each screen could observe and mutate independently.

yes, `provides` in a `Providers(...) { }` call works like `to` in `mapOf(...)`

it works like
```Providers(foo provides bar) {
  if (foo.current == bar) // this will be true```

just as
```val myMap = mapOf(foo to bar)
if (myMap[foo] == bar) // this will be true```

ambients are keys into a composition-local persistent (in the persistent data structure sense) map.

if you would like screen2 to be able to edit data that screen1 can see, it might conceptually look something like this:
```val sharedState = remember ( MyState() }
when (sharedState.currentScreen) {
  Screens.One -&gt; Screen1(sharedState)
  Screens.Two -&gt; Screen2(sharedState)
}```

and then `MyState` would offer an API that Screen1 and Screen2 can use

using ambients here is likely not what you want, as you're creating hidden dependencies and requirements that are harder to reason about

So that means `Providers` will only work for children but we can't return data from providers in parent node of a tree ?

Correct. You can provide a mutable object that other things can observe changes to but that's the most you can do in this regard. Ambients don't change the top down ownership of data, they only allow you to provide data implicitly