IMHO the key is to minimise the potential for closing over state that isn't
available to a future's callback. This is tricky, and the approach I'm
going to suggest only diminishes the risk, it does not eliminate it.
I see that there are broadly two options: either create a worker actor to
manage your asynchronous action; or use pipeTo as Michael suggests.
Using a worker actor in place of the future isn't always under your control
given that the future is yielded by some other library; as appears to be
the case for you. Which leaves you pipeTo...
The thing to manage it transforming the result of the future into a form
that your actor can receive and continue with i.e. you may need to pass
context. It is this additional context that you must be careful about
constructing in order to avoid closing over state that isn't available to
your callback. However given that you're just performing a transformation,
the risk of closing over something is lessened. Here is an example
(absolutely not tested/compiled/styled etc.):
case UpdateState => {
val tran = rClient.transaction()
(tran.zcard(key)
mapTo (z => (tran, key, z))
recover {case f => log.warning("ZCARD future failed ...", f)}
pipeTo self)
tran.exec()
case (tran: Transaction, key: String, z: Int) =>
(tran.zrange(key, z - 1, z)
recover {case e => log.warning("ZRANGE future failed ...", e)}
pipeTo self)
case x: ByteString =>
val v = x.utf8String
log.info(s"Updating state with $v ")
mutableState ++ v
--
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