make join faster #359

Signed-off-by: Stuart Halloway <stu@thinkrelevance.com>

src/clj/clojure/string.clj

@@ -70,8 +70,17 @@
 (defn ^String join
   "Returns a string of all elements in coll, separated by
   separator.  Like Perl's join."
-  [^String separator coll]
-  (apply str (interpose separator coll)))
+  ([coll]
+     (apply str coll))
+  ([separator [x & more]]
+     (loop [sb (StringBuilder. (str x))
+            more more
+            sep (str separator)]
+       (if more
+         (recur (-> sb (.append sep) (.append (str (first more))))
+                (next more)
+                sep)
+         (str sb)))))
 
 (defn ^String chop
   "Removes the last character of string, does nothing on a zero-length

test/clojure/test_clojure/string.clj

@@ -15,9 +15,16 @@
   (is (= "FOObarfoo" (s/replace-first-by #"foo" s/upper-case "foobarfoo"))))
 
 (deftest t-join
-  (is (= "1,2,3" (s/join \, [1 2 3])))
-  (is (= "" (s/join \, [])))
-  (is (= "1 and-a 2 and-a 3" (s/join " and-a " [1 2 3]))))
+  (are [x coll] (= x (s/join coll))
+       "" nil
+       "" []
+       "1" [1]
+       "12" [1 2])
+  (are [x sep coll] (= x (s/join sep coll))
+       "1,2,3" \, [1 2 3]
+       "" \, []
+       "1" \, [1]
+       "1 and-a 2 and-a 3" " and-a " [1 2 3]))
 
 (deftest t-chop
   (is (= "fo" (s/chop "foo")))