ryoakg · June 29, 2016 15:12 · ryoakg · Jun 29, 2016
diff --git a/apply_ctor.clj b/apply_ctor.clj
 (ns apply-ctor
  (import [java.lang.reflect Constructor]))

 (defn- acceptable-types? [ptypes atypes]
  (and (= (count ptypes) (count atypes))
       (every? (fn [[ptype atype]]
                 (or (= ptype atype)
                     ((ancestors atype) ptype)))
               (map vector ptypes atypes))))

 (defn apply-ctor [^Class klass args]
  (let [atypes (into-array Class (map class args))
        ctors (for [^Constructor ctor (.getConstructors klass)
                    :let [ptypes (.getParameterTypes ctor)]
                    :when (acceptable-types? ptypes atypes)]
                ctor)]
    (when (empty? ctors)
      (throw (IllegalArgumentException.
              (str "No matching ctor found for " klass))))
    (let [^"[Ljava.lang.Object;" args (into-array Object args)]
      (.newInstance ^Constructor (first ctors) args))))
diff --git a/test.clj b/test.clj
 (defn f1 [c args] (eval `(new ~c ~@args)))
 (defn f2 [c args] (apply-ctor c args))

 (time (dotimes [i 10000] (f1 String [(str "hoge" i)])))
 ;; "Elapsed time: 4497.773954 msecs"

 (time (dotimes [i 10000] (f2 String [(str "hoge" i)])))
 ;; "Elapsed time: 461.229971 msecs"
	(ns apply-ctor
	(import [java.lang.reflect Constructor]))

	(defn- acceptable-types? [ptypes atypes]
	(and (= (count ptypes) (count atypes))
	(every? (fn [[ptype atype]]
	(or (= ptype atype)
	((ancestors atype) ptype)))
	(map vector ptypes atypes))))

	(defn apply-ctor [^Class klass args]
	(let [atypes (into-array Class (map class args))
	ctors (for [^Constructor ctor (.getConstructors klass)
	:let [ptypes (.getParameterTypes ctor)]
	:when (acceptable-types? ptypes atypes)]
	ctor)]
	(when (empty? ctors)
	(throw (IllegalArgumentException.
	(str "No matching ctor found for " klass))))
	(let [^"[Ljava.lang.Object;" args (into-array Object args)]
	(.newInstance ^Constructor (first ctors) args))))
	(defn f1 [c args] (eval `(new ~c ~@args)))
	(defn f2 [c args] (apply-ctor c args))

	(time (dotimes [i 10000] (f1 String [(str "hoge" i)])))
	;; "Elapsed time: 4497.773954 msecs"

	(time (dotimes [i 10000] (f2 String [(str "hoge" i)])))
	;; "Elapsed time: 461.229971 msecs"