Okay I ve been staring at this too long Am I missing somethi

Question

Okay I ve been staring at this too long Am I missing something basic here Why can t I do `myMap value MyType A = listOf MyThing 1 MyThing 2 ` `myMap value MyType B = listOf MyThing 3 MyThing 4 ` `myMap value MyType C = listOf MyThing 5 MyThing 6 ` with a map defined of `val myMap = MutableStateFlow lt Map lt MyType List lt MyThing gt gt gt emptyMap `

Chris Lee · Answer

That value doesn t seem right though am unfamiliar with that map impl

Vampire · Answer

I d say `Map` vs `MutableMap`

Colton Idle · Answer

face palm

Colton Idle · Answer

Looks like my eyesw kept going to MutableStateFlow and thinking that it should be fine to be mutated

Colton Idle · Answer

I wonder if MutableStateFlow with a MutableMap is fine

Wout Werkman · Answer

I would not recommend using MutableMap inside MutableStateFlow Whoever observes the flow will not observe changes in the MutableMap While in theory it s possible to design your flows with this in mind nesting mutable data is generally considered a bug magnet

Wout Werkman · Answer

In the example you showed here the value might be updated in between the insertions you make into the map This could make that 1 You insert the `MyType A` entry into one map 2 `myMap value` get s updated from another thread 3 You insert the `MyType B` and `MyType C` entries into the new map 4 The new map is now missing the `MyType A` entry

Wout Werkman · Answer

You could achieve the same semantics without race conditions as follows ```val myMap = MutableStateFlow lt Map lt MyType List lt MyThing gt gt gt emptyMap myMap update oldValue gt oldValue + mapOf MyType A to listOf MyThing 1 MyThing 2 MyType B to listOf MyThing 3 MyThing 4 MyType C to listOf MyThing 5 MyThing 6 ```

Colton Idle · Answer

hm cant seem to get something like that to compile i ll keep trying maybe some extension function isn t making it s way it one last question though is there a way to be able to set the data in this sort of way Where I can udpate a specific item in the map vs adding to the map myMap value MyType A = listOf MyThing 1 MyThing 2

Chris Lee · Answer

yes mutable maps support the operator and assignment Won t work if map is not mutable

Wout Werkman · Answer

No it won t work on immutable maps It s always recommended to use `update` ```myMap update it + MyType A to listOf MyThing 1 MyThing 2 ``` You can wrap it in a utility function ```operator fun MutableStateFlow lt Map lt MyType List lt MyThing gt gt gt set key MyType value List lt MyThing gt Unit = update it + key to value myMap MyType A = listOf MyThing 1 MyThing 2 ```

Francesc · Answer

if you use a mutable map or list on the state flow it won t emit when you make changes to it because internally the state flow is comparing it against the current value which is the same so nothing gets emitted