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.
