Is there an existing Flow method like this? I don’...

# flow

[Chris Fillmore]

Is there an existing Flow method like this? I don’t see one, just curious if I’m missing it.

fun <T> Flow<T>.onChange(action: (oldValue: T, newValue: T) -> Unit): Flow<T>

[Chris Fillmore]

Similar to Delegates.observable

[wasyl]

Perhaps you can achieve what you want with runningFold or runningReduce?

[Chris Fillmore]

Ooh good idea

[Chris Fillmore]

Thanks for the tip, I’ll try it out

[ephemient]

I could also imagine either one of these, similar to Iterable extensions,

fun <T> Flow<T>.zipWithNext(): Flow<Pair<T, T>>
fun <T, R> Flow<T>.zipWithNext(action: suspend FlowCollector<R>.(oldValue: T, newValue: T) -> Unit): Flow<R>

or a modification of distinctUntilChangedBy,

fun <T> Flow<T>.distinctUntilChangedWith(predicate: (T, T) -> Boolean): Flow<T>

to be proposed as additions to Flow

[Chris Fillmore]

Fwiw this is what I implemented

fun <T> Flow<T>.onChange(action: suspend (oldValue: T, newValue: T) -> Unit): Flow<T> {
    return runningReduce { old, new ->
        action(old, new)
        new
    }
}

[Chris Fillmore]

I named it onChange just because in my particular case I’m dealing with state changes in a StateFlow, but another name might be more suitable to a general purpose Flow