OK that makes more sense, BeamFn is not an interface. I imagine they argued about that decision at some point.
In your example, MyFn looks to be a general class as it can work with any clojure var. Do you have a package with many of these type of stub classes defined? I mean, you could name it BeamFnIntegerString thus encoding the specializations of the baseclass into the type. One of my questions was about the range of types that end up specializing the BeamFn<>. Great link about the proxy attack, that is very interesting. I want to dive into that one a bit more. On Tue, Jul 2, 2019 at 8:14 PM atdixon <atdi...@gmail.com> wrote: > I'm glad someone else is thinking on this too! > > #2 - For my case at the moment (Apache Beam), I believe we will always > know the types in advance so using a Java class is workable but of course a > (proxy++) would be ideal. Beam asks for us to extend abstract generic class > so we must use (proxy). It also asks for our instances to be Serializable > (again, proxy explicitly refuses to help here > <https://clojure.atlassian.net/browse/CLJ-2204> but I believe this, too, > should be surmountable, without the security implications of that link). In > any case, what we do looks like this: > > // pseudo-ish code > public class MyFn extends BeamFn<Integer, String> implements Serializable > { > public MyFn(Var fn) { this.fn = fn; } > @Override public String invoke(Integer input) { return (String) fn. > invoke(input); } > } > > On the Clojure side: > > ;; pseudo-ish code > > (defn my-fn [^Integer val] ...return a string...) > > ... > (register-beam-step (MyFn. #'my-fn)) > ... > > Note how we pass the Clojure function as a Var; this is b/c Beam wants to > send the function over the wire. IFn is not serializable; Var is however > and can be resolved back to Clojure function on the other end during > deserialization. > > Now of course this whole dance could be eliminated with a specialized > library that included a proxy++ function that included the ability for > clients to specify generic type parameter values and serialization support > (the mechanics of which would need ironing out but I think should be > possible.) > > And to your point about types not known at runtime... this proxy would > support that use case on-the-fly, which opens a bunch of possible > interesting options, as well. > > > On Tuesday, July 2, 2019 at 8:24:41 PM UTC-5, Chris Nuernberger wrote: >> >> eglue, >> >> 1. I think this is a great idea if it is really necessary. I would be >> in favor of a reify++ alone to simplify things. I find reify amazing at >> code compression and heavily use it via type specific macros to implement >> interfaces that for instance support a particular primitive type. >> 2. Is a possible workaround to define java interfaces that implement the >> type specific generic interfaces and then reify those explicitly or is the >> set of possible interface specialization types unknown a-priori? >> 3. The case where something is unbounded or unknown a-priori I would >> think would often end up with a java class as on of the specializations. >> In this case, regardless of the cause, one answer might be an upgraded >> reify pathway. >> 4. Are these perhaps cases where you can create just a little bit of >> java as a generator somehow to generate the interface you need to reify? >> >> >> I would personally find reify a much nicer pathway than calling clojure >> vars from java. >> >> I also think there could be low hanging fruit (or just good unknown >> libraries) in the pathway for calling clojure vars from java. >> >> >> Interesting problem (at least to me), thanks! >> >> On Thu, Jun 20, 2019 at 10:03 PM eglue <atd...@gmail.com> wrote: >> >>> Don't get me wrong, I'm as much against types as the next R̶i̶c̶h̶ >>> ̶H̶i̶c̶k̶e̶y̶ guy. >>> >>> However -- there are many popular Java frameworks that love to reflect >>> on their annotations and their generic type signatures. >>> >>> To name a heavyweight: Spring. But also, of late: big data frameworks, >>> many written in Java, love reflecting on generic type signatures. My org is >>> looking at Beam and Flink, for example. >>> >>> These frameworks use types not for the static checking really but as >>> parameters governing their own dynamic behavior. For example, Spring will >>> use types at runtime to simply match objects to where they should be >>> dynamically injected. Beam will look at your type signatures and do runtime >>> validations to ensure it can process things appropriately. Of course this >>> is unfortunate, using types this way, when it is all really just data. >>> Clojure does -- or would do -- it better, simpler, directer, and all of >>> that. >>> >>> Yet we would like to leverage these frameworks. Or rather, we must for >>> various pragmatic and business reasons. >>> >>> And any time we need to "communicate" to these frameworks "through" >>> their desired fashion of generic types and annotations, we can, of course, >>> create the appropriate .java files to represent what is needed (and then do >>> the invocation back to Clojure via IFn.invoke or Compiler.eval, etc). Yes, >>> this works. >>> >>> However this is quite tedious because in these frameworks I mentioned >>> you end up having to create these Java files quite a bit. For example, when >>> expressing a streaming data pipeline to Beam, you may specify multiple >>> transforms, each a function with its own type signature. >>> >>> A little searching and it seems Clojure has shied away from generating >>> generic type information in places where it could offer this capability. >>> >>> For example, in `proxy` ... or I suppose also in `gen-class`, `reify`, >>> and other dynamic bytecode generation features of Clojure. >>> >>> However it seems to me that `proxy` (and these others) could allow one >>> to pass in a representation of desired type arguments, annotations, etc. >>> and then we could remain in Clojure to interop with these popular >>> frameworks. >>> >>> I respect Clojure's efforts to keep its core small and wait for worthy >>> features to prove themselves. >>> >>> So my question is not when is Clojure going to do this, but rather: >>> >>> Are there any precedents in the community for someone building out the >>> kind of richer Java interop that I'm nodding toward here? >>> >>> For example, does anyone know of an attempt out there to build a `proxy` >>> plus-plus, that would allow one to extend a generic class with provided >>> type parameters and have this metadata properly rendered in the bytecode >>> that proxy produces? >>> >>> If not, as a practical and hopefully quick and workable solution, I was >>> thinking it'd be possible to take the bytecode emitted by proxy and re-run >>> it through ASM to create a *new* class with simply the proxy-produced class >>> bytes filled-in with the desired, provided type parameters. I bet this >>> could be sufficient and fast, with the slight overhead of the extra class. >>> >>> To do this, I think I'd need access to these proxy-made bytes... either >>> by having proxy answer them somehow, or offering a hook to contribute to >>> the defined bytecode before it is committed to the classloader, or by >>> having DynamicClassLoader have these bytes on hand for inquiring parties, >>> or something else along these lines. This would likely be something that >>> Clojure core would have to expose .. correct me if I'm wrong. >>> >>> Would love to hear any other immediate thoughts on this. >>> >>> I think once you realize that this generic type information is not even >>> being used for "static typing" by these frameworks but rather as an (albeit >>> poor) means to receive semantic information from their clients (as >>> parameters to govern their own dynamic behavior), then the need/value of >>> being able to remain in Clojure and communicate to these libraries through >>> generic params and annotations perhaps becomes more understandable.. >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> -- >>> You received this message because you are subscribed to the Google >>> Groups "Clojure" group. >>> To post to this group, send email to clo...@googlegroups.com >>> Note that posts from new members are moderated - please be patient with >>> your first post. >>> To unsubscribe from this group, send email to >>> clo...@googlegroups.com >>> For more options, visit this group at >>> http://groups.google.com/group/clojure?hl=en >>> --- >>> You received this message because you are subscribed to the Google >>> Groups "Clojure" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to clo...@googlegroups.com. >>> To view this discussion on the web visit >>> https://groups.google.com/d/msgid/clojure/128dd732-b79e-4c35-999f-691cdc42512b%40googlegroups.com >>> <https://groups.google.com/d/msgid/clojure/128dd732-b79e-4c35-999f-691cdc42512b%40googlegroups.com?utm_medium=email&utm_source=footer> >>> . >>> For more options, visit https://groups.google.com/d/optout. >>> >> -- > You received this message because you are subscribed to the Google > Groups "Clojure" group. > To post to this group, send email to clojure@googlegroups.com > Note that posts from new members are moderated - please be patient with > your first post. > To unsubscribe from this group, send email to > clojure+unsubscr...@googlegroups.com > For more options, visit this group at > http://groups.google.com/group/clojure?hl=en > --- > You received this message because you are subscribed to the Google Groups > "Clojure" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to clojure+unsubscr...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/clojure/6c1a93e7-b25b-4199-a41a-9308b231ffc1%40googlegroups.com > <https://groups.google.com/d/msgid/clojure/6c1a93e7-b25b-4199-a41a-9308b231ffc1%40googlegroups.com?utm_medium=email&utm_source=footer> > . > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "Clojure" group. 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