Fluid Dynamics <a2093...@trbvm.com> writes: > On Saturday, January 24, 2015 at 1:43:15 PM UTC-5, Elric Erkose wrote: >> >> Hello, >> >> I have an app which specifies a protocol and a record name. At runtime, it >> searches the classpath for files implementing the specification and creates >> a map of namespace to instance for each. Before I implemented the protocol, >> I just specified function names. I was able to lookup the function names >> and call them. After I switched to using a protocol, I get a >> CompilerException. >> >> Here's the question: How do I instantiate a known record from an unknown >> namespace? >> >> Here is the sample code. Thanks for you help. >> >> ```clojure >> (ns proto) >> >> (defprotocol Proto >> (meth [this])) >> >> ;; use clojure.tools.namespace.find to locate the namespace. >> ;; for simplicity, we just def it here. >> (def that 'rec) >> >> (require that) >> >> ;; the symbol "Rec" is part of the specification >> (let [inst (ns-resolve that (symbol "Rec"))] >> (when (class? inst) >> (println "inst:" (type inst) inst) >> ;; => java.lang.Class rec.Rec >> >> (println "meth:" (meth (new rec.Rec))) >> ;; => it works when I know it. >> >> ;; uncomment this for a CompilerException >> ;;(println "meth:" (meth (new inst))) >> ;; => CompilerException java.lang.IllegalArgumentException: >> ;; Unable to resolve classname: inst, compiling:(proto.clj:21:28) >> )) >> ``` >> >> ```clojure >> (ns rec >> (:require proto)) >> >> (defrecord Rec [] >> proto.Proto >> (meth [this] "it works when I know it")) >> ``` >> > > The new special form doesn't evaluate its argument, so "inst" results in > looking for a classname of "inst", not whatever inst is bound to. (eval > `(new ~inst)) might work though. > > -- > 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.
Using `eval' here is like shooting sparrows with cannons. While I despise the latter and wouldn't help with that, a better solution for the former is the `newInstance' method of java.lang.Class: (let [c java.lang.String] (.newInstance c)) ; => "" -- 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.
signature.asc
Description: PGP signature
