I have a `MutableStateFlow<Map<..., ...>>` what’s the most idiomatic way to mutate the ...

# coroutines

[William Reed]

I have a MutableStateFlow<Map<..., ...>>

what’s the most idiomatic way to mutate the map and update the StateFlow ? seems like I need to make a copy of the current value and then update it?

something like this seems verbose and awkward

stateFlow.value = stateFlow.value.toMutableMap().apply { … modify …}

[William Reed]

i could do this

inline fun <K, V> MutableStateFlow<MutableMap<K, V>>.mutate(mutation: (MutableMap<K, V>) -> Unit) {
    val newValue = value.toMutableMap()
    mutation(newValue)
    value = newValue
}

and usage would just be

stateFlow.mutate {
  ... modify ...
}

[melatonina]

It's the same problem as replacing any observable collection with StateFlow, for example when using a RecyclerView on Android. Inexplicably, I never saw this addressed anywhere. I'm not an expert, though.

[Nick Allen]

I suggest MutableStateFlow<Map<K, V>>. You can update it with just stateFlow.value += item or something similar. If you need more complicated mutations, then i think you are stuck with more complicated code.