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I have implemented a typed Android data flow that instead of `val currentState: UIState?` provides `val typedState: T`, with `&lt;T : UIState&gt;` as the generic type and it throws if the current state is `null`. Is this something you think is useful in some form? I can make a PR. Another idea could be to pull this up to a new `TypedDataFlow` interface. Worth the consideration, what are your thoughts on this?

Interesting question here, as we usually  setup a first inital data

I think we never have a null state to start

but concerning the action functions, it can arrive that we don’t return any new state

The crux is what you say: _usually_
So we could have two types of `DataFlow`: typed and untyped. The current impl is untyped, the typed one has generic type `&lt;T : UIState&gt;` and can never be null. We could also have a nullable typed version.

The nonnullable version must guarantee that the state getter(s) always return nonnull state

If used with a user's own sealed class hiearachy of `UIState`, then this allows for some powerfull state machine modelling

2 things I have in mind, and perhaps confirm what you say:
• there is always a type for the flow (sealed class of states), an empty state at minmum
• an action can return null to not update finally anything

the thing also is to allow to reuse generic states like Loading, Fail or Empty

then a DataFlow has a strong type, but you can push any event that is in your DataFlow type hierarchy

your sealed class, including the generic states