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Title
p

Pedro Alberto

12/07/2021, 2:24 PM
on question not sure if you know the reason: so in android we use StateFlow and usually we use MutableStateFlow but the fragment only has the readonly so we created a function like this
val <T> MutableStateFlow<T>.readOnly
    get() = this as StateFlow<T>
now I realised there is a function called asStateFlow() but when you go into asStateFlow the function does something different
public fun <T> MutableStateFlow<T>.asStateFlow(): StateFlow<T> =
    ReadonlyStateFlow(this, null)
m

mkrussel

12/07/2021, 2:30 PM
The
ReadonlyStateFlow
is so consumers of the flow cannot cast back to
MutableStateFlow
and change the values. Similar to
unmodifiableList
in Java.
🙌 1
p

Pedro Alberto

12/07/2021, 2:33 PM
what would you do @mkrussel? cast or asStateFlow
m

mkrussel

12/07/2021, 2:37 PM
I would go with
asStateFlow
p

Pedro Alberto

12/07/2021, 2:38 PM
ok it’s funny cus there docs also have comments like
// Backing property to avoid state updates from other classes
    private val _uiState = MutableStateFlow(LatestNewsUiState.Success(emptyList()))
m

mkrussel

12/07/2021, 2:38 PM
But the cast would be a bit more performant and if you trust the consumers not to cast back then it would be just as safe
p

Pedro Alberto

12/07/2021, 2:39 PM
that’s why I’m asking cus the thing is per state and shareflow we would create an extra object
m

mkrussel

12/07/2021, 2:39 PM
The backing property is needed for both solutions. One is more paranoid then the other, but both accomplish the desired goal.
My thought is one object is tiny, but others are more conservative about memory.
p

Pedro Alberto

12/07/2021, 2:47 PM
thanks @mkrussel really nice to share 🙂 have a nice day
a

Adam Powell

12/07/2021, 3:28 PM
"one object is tiny" but no object is free. 🙂 Tiny * 1000 is not so tiny anymore. 0 * 1000 is 0.
On mobile, "little" CPU cores execute instructions in order. Indirection is a lot more expensive than it looks. Performance death by a thousand cuts because all of your code is just a little bit inefficient is very real.
When doing the more efficient thing is no more cumbersome than being inefficient, there's no good reason not to form and exercise good habits.
p

Pedro Alberto

12/07/2021, 3:46 PM
thanks @Adam Powell for your opinion we actually decided to go with my simple extension function
val <T> MutableStateFlow<T>.readOnly
    get() = this as StateFlow<T>
since we use sharedflow and sateflow everywhere and if we sum up it could have impact on a long run.