Giovanni, On Mon, Feb 16, 2015 at 9:37 PM, Giovanni Alberto Caporaletti < [email protected]> wrote:
> What I'm saying is that conceptually having a single item or a stream are > two different things and this should be reflected in the type system (e.g. > rx Task). > I disagree and let me tell you why :) Think about it—Stream subsumes Future: there is no type that reflects an empty stream, there is no type that discerns bounded from unbounded streams, hot or cold streams, no type for bounded streams of size N, no type for this is a stream that fails after N elements… If you were to provide types for all these very important >>shapes<< of streams you'd end up executing the streams inside the compiler when you try to typecheck the program. > What you're suggesting is implementation details, the assumption that a > source will only emit 1 item is nowhere to be seen in the type. > if I have a signature that returns (or takes) a Stream[T] I don't see the > constraint that that stream will never have more than 1 item. > > A Future is a very different animal from the Stream, especially because it > represents a computation that's already happening. > The statement regarding Future is provably false: Let me present Exhibit A: val p = Promise[Pigdog]() val f = p.future // is f an already running computation? One of the most prevalent misconceptions is that Futures are inherently about computation—they're not :) Future are about facts which may or may not be available at a specific point in time. I think the source of the confusion is twofold: Future.apply and Future.<transformations>, in fact, if Future only had the `onComplete` method one could create typeclasses that would provide -all- of the functionality already available for Future (of course given that Promise allows for populating it with a value). > I have no way (afaik) of expressing in a type signature that "this is a > blueprint for a source of a single (or zero) item". > > Look at the rx Observable.single method. It does that but it doesn't > express it in the type system (as Task does). A lot of use cases involve > Observables/Producers/Sources that can possibly have only one item, hence > this PR: https://github.com/ReactiveX/RxJava/pull/2641. > > But don't get me wrong, it doesn't mean that Future (or rx.Task) isn't useful, quite the contrary, but stream is provably more useful (since it supports more usecases). > > On Monday, 16 February 2015 18:41:07 UTC, Jim Hazen wrote: >> >> These days the current API supports a number of ways of constructing a >> Source. >> >> http://doc.akka.io/api/akka-stream-and-http-experimental/ >> 1.0-M3/?_ga=1.72893075.1209102577.1407799351#akka.stream.scaladsl.Source$ >> >> Based upon these available methods, if I needed to supply 0 or 1 elements >> based upon some business logic, I would probably create a custom iterator >> implementation. Your business logic can then determine whether to emit an >> element or provide hasNext=false, which I believe will signal that the >> source is empty and trigger a teardown of the materialized flow. >> > -- > >>>>>>>>>> Read the docs: http://akka.io/docs/ > >>>>>>>>>> Check the FAQ: > http://doc.akka.io/docs/akka/current/additional/faq.html > >>>>>>>>>> Search the archives: https://groups.google.com/group/akka-user > --- > You received this message because you are subscribed to the Google Groups > "Akka User List" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > Visit this group at http://groups.google.com/group/akka-user. > For more options, visit https://groups.google.com/d/optout. > -- Cheers, √ -- >>>>>>>>>> Read the docs: http://akka.io/docs/ >>>>>>>>>> Check the FAQ: >>>>>>>>>> http://doc.akka.io/docs/akka/current/additional/faq.html >>>>>>>>>> Search the archives: https://groups.google.com/group/akka-user --- You received this message because you are subscribed to the Google Groups "Akka User List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/akka-user. For more options, visit https://groups.google.com/d/optout.
