timeout+collector operator

[CLOVIS-AI]

Use case

Flow has the timeout operator. When the timeout is reached, a TimeoutCancellationException is thrown into the Flow. Typical usage seems to be to catch the thrown exception to perform additional processing (from the .timeout kdoc):

.timeout(100.milliseconds).catch { exception ->
    if (exception is TimeoutCancellationException) {
        // Catch the TimeoutCancellationException emitted above.
        // Emit desired item on timeout.
        emit(-1)
    } else {
        // Throw other exceptions.
        throw exception
    }
}

This is a bit unwieldy. What about having an overload for this specific case?

Declaration:

fun <T> Flow<T>.timeout(duration: Duration, block: FlowCollector<T>.() -> Unit): Flow<T>

Usage (same behavior as above):

.timeout(100.milliseconds) {
    emit(-1)
}

---

This came up as a user of one of my libraries (Pedestal Cache), which is entirely Flow-based, attempted to represent "Get the latest value from the cache, substituting a default value if the request takes too long".

[dkhalanskyjb]

Duplicate of #4143