You've understood correctly - you'd need to create an instantiator for each different set of argument types.
Whether this suits you or not will depend on your use case: however in the (possible quite common?) situation that you are doing a lot of runtime instantiation using the same argument types then I think it is a big win. You can also still define new-instance in terms of the instantiator if you like, using something like: (defn new-instance "Create a new instance of the specified class with the given args." [^Class c & args] (apply (apply instantiator c (map class args)) args)) On Thursday, 4 July 2013 13:37:04 UTC+1, Jim foo.bar wrote: > > hmm...unless I've understood wrongly, that would be 'once per type, > arity and potentially argument-types'...so yes, for all your Doubles you > would pay it once, for all your Longs once more etc etc...if you start > doing it with objects with more than one ctor arity and possibly same > arities but with different arg-types then I don't see how the instantiator > would know about all potential possibilities. I mean it's not generic > anymore... > > have I completely misunderstood you? can you show a sample/overview of the > 'instantiator' fn you're referring to? > > thanks, > > Jim > > > On 04/07/13 13:04, Mikera wrote: > > Both are somewhat problematic from a performance perspective. > > I'd actually be tempted to do this in a "higher order function" style > that returns a compiled construction function for the correct argument > types, e.g. something like > > (def double-builder (instantiator Double Long)) > (double-builder 2) > => 2.0 > > This allows you to take the pay the cost of compilation / reflection > only once. > > On Thursday, 4 July 2013 11:57:32 UTC+1, Jim foo.bar wrote: >> >> (defmacro instantiate >> "Returns an instance of the given class. Depending on the argument list will >> invoke the corresponding constructor." >> [cl-name & args] >> `(eval (list 'new ~cl-name ~@args))) >> >> (defn new-instance "Create a new instance of the specified class using >> reflection." >> [^Class c & args] >> (if (empty? args) (.newInstance c) >> (.newInstance >> (.getConstructor c (into-array (map class args))) >> (to-array args)))) >> >> >> any particular preference? >> >> Jim >> >> -- > -- > 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 <javascript:> > Note that posts from new members are moderated - please be patient with > your first post. > To unsubscribe from this group, send email to > clojure+u...@googlegroups.com <javascript:> > 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+u...@googlegroups.com <javascript:>. > For more options, visit https://groups.google.com/groups/opt_out. > > > > > -- -- 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/groups/opt_out.
