You mean (supers (type %)) ?
Sean Corfield -- (904) 302-SEAN An Architect's View -- http://corfield.org From: larry google groups Sent: Monday, December 23, 2013 7:28 PM To: clojure@googlegroups.com I find this surprising. I do this: (supers %) inside of my :post condition, and I get: java.lang.ClassCastException: clojure.lang.PersistentHashMap cannot be cast to java.lang.Class at clojure.core$bases.invoke(core.clj:4985) at clojure.core$supers.invoke(core.clj:4994) at admin.secretary$fetch.invoke(secretary.clj:327) How else do I find what interfaces the return value might be implementing? On Monday, December 23, 2013 10:04:54 PM UTC-5, larry google groups wrote: > enforce that the return is a subtype of java.util.Map rather than checking > for a specific concrete class of map. Thank you. I'll do that. All the same, can anyone tell me why this function changes the type of the value? All it does is call "fetch". The fetch function has this post condition: :post [(= (type %) clojure.lang.PersistentHashMap)]} And "get-distinct" has the same restriction, but in get-distinct I get this error: java.lang.AssertionError: Assert failed: (= (type %) clojure.lang.PersistentHashMap) at admin.controller$get_distinct.invoke(controller.clj:40) The :post condition of "fetch" does not throw an error, so I know that "fetch" is returning clojure.lang.PersistentHashMap. However, when I print the return type of get-distinct, I am amazed to see that it is now clojure.lang.PersistentArrayMap. This function does almost nothing, so I am surprised it changes the concrete implementation type of the return value. On Monday, December 23, 2013 3:43:09 AM UTC-5, Cedric Greevey wrote: The two classes have essentially the same semantics, but performance differences, which is why Clojure sometimes uses one and sometimes the other. If you want to enforce that a map is returned, enforce that the return is a subtype of java.util.Map rather than checking for a specific concrete class of map. On Sun, Dec 22, 2013 at 3:07 PM, larry google groups <lawrenc...@gmail.com> wrote: Hmm, I see. get-distinct was returning an empty lazyseq, which apparently made the difference. On Sunday, December 22, 2013 2:56:01 PM UTC-5, larry google groups wrote: Hmm, the different return types seem tied to the 2 different functions being called, but both functions have the same return type, which is a lazyseq. I am using Monger to get data from MongoDb. These functions are private: (defn- get-distinct [request] {:pre [(= (type request) clojure.lang.PersistentHashMap)] :post [(= (type %) clojure.lang.LazySeq)]} (monger/get-distinct (:item-type request))) (defn- paginate-results [request] {:pre [ (= (type request) clojure.lang.PersistentHashMap)] :post [(= (type %) clojure.lang.LazySeq)]} (monger/paginate-results (:item-type request) (if (:which-page request) (:which-page request) 0))) Both of these functions return lazyseqs, as expected. The results from both get run through a (reduce) function that does some minor filtering. Yet in one case the return type (from the reduce function) is clojure.lang.PersistentArrayMap and in the other it is clojure.lang.PersistentHashMap. I'd like to be able to write a :post condition that enforces strictness, but that seems impossible because I can not figure out what the rule is that handles the conversion. I don't care if the return type is clojure.lang.PersistentArrayMap or clojure.lang.PersistentHashMap, all I want is it for it be consistently one or the other. On Sunday, December 22, 2013 2:31:45 PM UTC-5, larry google groups wrote: I am surprised that a map literal is clojure.lang.PersistentArrayMap but as soon as I assign it to a var, it becomes clojure.lang.PersistentHashMap. Are there any rules for being able to predict when these conversions occur? user> (type {}) clojure.lang.PersistentArrayMap user> (type {:what "why?"}) clojure.lang.PersistentArrayMap user> (def curious {:what "why?"}) #'user/curious user> (type curious) clojure.lang.PersistentHashMap user> (def sug (assoc curious :whodoneit "mikey")) #'user/sug user> (type sug) clojure.lang.PersistentHashMap I am curious because I wrote a (reduce) function which mostly just builds a map: (assoc map-of-data (:item-name next-item) next-item)) Since I was using assoc I was certain I would get clojure.lang.PersistentHashMap back, but instead I got clojure.lang.PersistentArrayMap. -- -- 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. 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