Thanks for the reply Gary. Sounds like I'm on as good a track as I can be with current Clojure.
I am curious though why you say that it is unrealistic for IFn to support arbitrary @FunctionalInterface. It certainly seems like it would require compiler changes, but I would think that either through emitting bytecode closer to Java 8 lambdas or through some form of type coercion it would possible. For example, Groovy just coerces their Closures to any Single Abstract Method type. I'm not sure how java.util.function.* as protocols would work, but still would require implementing for each SAM you come across. IFn as a protocol seems to address a different interop use case. Maybe for receiving a Java lambda you want to use as if it's a Clojure function. Most of the Java interop from Clojure is slick (sometimes more clear than in Java itself), it would be unfortunate to leave functions as second-class citizens for interop. Granted, there may be a simplicity argument against this (maybe that's why Java varargs require an explicit array?). Andrew Oberstar On Mon, Jul 27, 2015 at 4:16 AM Gary Verhaegen <gary.verhae...@gmail.com> wrote: > On Sunday, 26 July 2015, Andrew Oberstar <ajobers...@gmail.com> wrote: > >> Hi, >> >> I'm wondering if anyone has a good approach for making calls from Clojure >> to Java APIs (e.g. Stream API) that expect a @FunctionalInterface type. >> >> Ideally, IFn would transparently work, but I'm guessing that requires >> some compiler changes. >> >> Right now, the best I can think of is a function or macro to reify a >> wrapper around a Clojure function to implement all of the usual interfaces >> from java.util.function. >> >> Anyone have any better ideas? >> >> Andrew Oberstar >> > > You're probably aware of this, but @FunctionalInterface is not a type, > it's an annotation. All it does is ensure, at compile time, that the > annotated element is an interface with a single non-default and non-static > method. At the type-system level, it's just an interface like any other, > and the lambda syntax is just a shorthand for an anonymous instance of a > well-defined type. > > Since the lambda syntax is java-compiler magic, you can't access it from > Clojure, and the most straightforward option right now is to actually know > which type is expected, e.g.: > > user=> (-> (doto (java.util.ArrayList.) (.add 1) (.add 2)) (.stream) (.map > (reify java.util.function.Function (apply [_ arg] (inc arg)))) (.collect > (java.util.stream.Collectors/toList))) > [2 3] > user=> > > As neither IFn nor Function are Clojure protocols, I do indeed think > you're best bet is a macro to essentially generate the above reify. You can > of course do a single macro that reifies to all of the protocols that you > need. > > I don't think it's realistic to hope that IFn will cover any arbitrary > @FunctionalInterface, as that is Java compiler magic. It may, in the > future, be extended to cover all of the standard ones in > java.util.function, or even all the ones in the standard library, but it's > not going to happen until Java 7 support is dropped. I guess the best you > could hope for in the short term would be to have IFn changed to a protocol. > > -- > 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. > 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. For more options, visit https://groups.google.com/d/optout.
