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Fast flow combination
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import kotlinx.coroutines.* | |
import kotlinx.coroutines.flow.* | |
private val undefined = Any() | |
internal fun <T> Iterable<Flow<T>>.combineLatest(): Flow<List<T>> = | |
combineLatest { it } | |
internal fun <T, R> Iterable<Flow<T>>.combineLatest(transform: suspend (value: List<T>) -> R): Flow<R> = flow { | |
class Update(@JvmField val index: Int, @JvmField val value: T) | |
val flows = toList() | |
var remainingCount = flows.size | |
var values: MutableList<Any?> = MutableList(remainingCount) { undefined } | |
channelFlow { | |
coroutineScope { | |
flows.forEachIndexed { index, flow -> | |
launch { flow.collectLatest { send(Update(index, it)) } } | |
} | |
} | |
}.collect { update -> | |
val index = update.index | |
val value = update.value | |
when { | |
remainingCount == 0 -> values = values.toMutableList() | |
values[index] === undefined -> remainingCount -= 1 | |
} | |
values[index] = value | |
if (remainingCount == 0) | |
@Suppress("UNCHECKED_CAST") | |
emit(transform(values as List<T>)) | |
} | |
} |
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