java - Clojure Reflection warning - call to write can't be resolved -

i'm struggling correct type hints avoid warn on reflection while writing text-file-output database query.

i've tried put ^string type hints before each function being called, output going hit text file on disk.

the reflection warning occurs on :row-fn line towards end of function. have comment reflection warning, dbdump/dbdump.clj:157:44 - call write can't resolved. on same line.

how can rid of warning? i'm thinking there performance cost when working large datasets.

(defn run-job [job-time-string db-spec config]   (let [; {{{         source-sql          (str "select * " (:source-base-name config)(:table-name config))         max-rows            (:max-rows            config)         fetch-size          (:fetch-size          config)         working-dir         (:working-dir         config)         output-name           (str working-dir "/" job-time-string ".pipe" )         field-delim         (:field-delim         config)         row-delim           (:row-delim           config)         log-report-interval (:log-report-interval config)         row-count           (atom 0)  ; state on rows         db-connection       (doto (j/get-connection db-spec))         statement           (j/prepare-statement db-connection source-sql :fetch-size fetch-size :concurrency :read-only :max-rows max-rows)         start-in-millis     (system/currenttimemillis)         replace-newline (^string fn [s]                           (if                               (string? s)                             (clojure.string/replace  s #"\n" " ")                             s)) ; i'd prefer not this; right can't load \n fields.         row-fn          (^string fn [v]                           (swap! row-count inc)                           (when                               (zero?                                (mod @row-count log-report-interval))                             (write-logs @row-count start-in-millis 3 (:table-name config) ))                           (str (join field-delim (doall (map #(replace-newline %) v))) row-delim ))         ]; }}}     (with-open [^java.io.writer wrtr (io/writer output-name )]         (info "fetching jdbc query..." )         (info source-sql)         (try           (j/query db-connection [statement]                    :as-arrays?    true                    :result-set-fn vec ; reflection warning, dbdump/dbdump.clj:157:44 - call write can not resolved.                    :row-fn        ^string #(.write wrtr (row-fn %)))           (catch exception e             (error (str "error while fetching jdbc data." (.getmessage e)))             (system/exit 9))))     (write-logs @row-count start-in-millis 0 (str (:source-base-name config)  (:table-name config) " completed - ")))) 

the reflection warning tells you need clarify write method called in #(.write wrtr (row-fn %)). you'll need type-hint wrtr , (row-fn %):

#(.write ^java.io.writer wrtr ^string (row-fn %)) 

incidentally, adding type hints fn forms or function literals has no effect. (well, adding primitive hints make resulting function implement relevant clojure.lang.ifn$[old]+ interface, hints need attached parameter vector and/or individual symbols naming parameters.)

(in contrast, adding type hints function names in defn forms have effect of placing :tag metadata on resulting vars; used compiler disambiguate java method calls.)