Could anyone please help me with understanding why `MutableStateFlow` would only emit last item in t...

# coroutines

[scana]

Could anyone please help me with understanding why MutableStateFlow would only emit last item in this example (running from Kotlin scratch file)?

val x = MutableStateFlow("Test")
CoroutineScope(<http://Dispatchers.IO|Dispatchers.IO>).launch {
    x.collect {
        println(it)
    }
}

x.value = "First"
x.value = "Second"
x.value = "Fourth"

println("Waiting...")
Thread.sleep(1000)

Result:

Waiting...
Fourth

[Joffrey]

State flows are conflated. Basically the fact that it's a StateFlow should mean that collectors should only care about the "current state" (or latest state). So the fact that you see all updates or just the last should be considered an implementation detail.

[Joffrey]

Now as to what exactly is happening here. You're using multiple threads here, so there is no guarantee the initial launch started collecting before you reach the sleep. What likely happens here is that the root coroutine blazes through the whole code and reaches Thread.sleep before the launched coroutine even started, so when the launch collects the flow, the flow is already in its last state.

[scana]

Thank you so much @Joffrey - great explanation. I actually now see this conflation being mentioned in the documentation 🤦

[ursus]

its a race, thats why, put sleep between .value = x, youll see more prints