clojure.core/memfn

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Type: macro Added: Clojure 1.0 Examples: 3 Runnable: 0

([name & args])

Expands into code that creates a fn that expects to be passed an object and any args and calls the named instance method on the object passing the args. Use when you want to treat a Java method as a first-class fn. name may be type-hinted with the method receiver's type in order to avoid reflective calls.

Examples

by nipra on 2010-07-16 . May have evaluation errors. ▶

(def *files* (file-seq (java.io.File. "/tmp/"))) #'user/*files* (count (filter (memfn isDirectory) *files*)) 68 (count (filter #(.isDirectory %) *files*)) 68 (count (filter java.io.File/.isDirectory *files*)) ; Clojure 1.12 or higher 68

by emidln on 2015-06-16 . May have evaluation errors. ▶

;; you must pass arguments to your method to add up to the expected arity (def starts-with (memfn startsWith prefix)) #'user/starts-with (starts-with "pikachu" "pika") true (starts-with "pikachu" "bulba") false

by reborg on 2018-07-30 . May have evaluation errors. ▶

(set! *warn-on-reflection* true) ;; memfn is inherently subject to reflective calls (time (dotimes [n 100000] (mapv (memfn toLowerCase) ["A" "B" "C"]))) ;; Reflection warning, call to toLowerCase can't be resolved ;; "Elapsed time: 794.081758 msecs" ;; But accepts and propagate type hints to avoid it (time (dotimes [n 100000] (mapv (memfn ^String toLowerCase) ["A" "B" "C"]))) ;; "Elapsed time: 33.708462 msecs"

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