Add support for Effects that dont change state

[sockeqwe]

At the moment you cannot do a piece of work without the need of returning a ChangeState object.

This proposal is about adding "effects". A typical use case for an Effect is triggering navigation without changing the state of the statemachine itself or doing some analytics tracking calls.

Proposed Syntax

inState<MyState> {
  onEnterEffect { stateSnapshot : MyState ->
       // Do something.
       Unit // return unit, no state change
   }

  onActionEffect<MyAction> action : MyAction, stateSnapshot : MyState ->
       // Do something.
       Unit // return unit, no state change
   }

  collectWhileInStateEffect(flowOf(1,2)) { value : Int, 
stateSnapshot : MyState ->
       // Do something.
       Unit // return unit, no state change
   }
}

Specs:

• Effects are suspending: i.e. signature lambda for onEnterEffect is suspend (State) -> Unit
• Effects dont get canceled when state transition happening.
• Effects are per default canceled when StateMachine CoroutineScope gets canceled. If you want to escape you can always use withContext(NonCancelable)

[gabrielittner]

Why do we need the explicit Unit that the effect returns?

[sockeqwe]

@gabrielittner you mean why it would not just return Any? instead of Unit or what do you mean exactly?

[gabrielittner]

More like, why does the lambda need to return anything at all?

[sockeqwe]

Hm, maybe I misunderstand you but what is the signature of such a lambda? What would you propose (can you give an example)?

[gabrielittner]

The signature would still be fun onEnterEffect(effect: (stateSnapshot : MyState) -> Unit), but the usage like this

onEnterEffect { stateSnapshot : MyState ->
   // Do something.
   // no Unit here
}

Effectively the same, I guess I was just confused by the explicit Unit as last line in your examples.

[sockeqwe]

👍 got it. Then we are talking about the same thing