Follow-up to “Simple String template replacement in Scala and Clojure”

Question

In my previous post, I showed a simple (naive) algorithm for doing a String template replacement.

One of the solutions, provided by mikera, seems like a much better algo

Answer 1

I think you are hit by reflection. *warn-on-reflection* is your friend. Here some tests with criterium.

replace-templates-original:         56.4us
replace-templates-original-hinted:   9.4us
replace-templates-new:             131.4us
replace-templates-new-hinted:        6.3us
replace-templates-very-new:          7.3us

Here is the replace-templates-very-new, a version I did myself for golf. :)

(defn replace-templates-very-new
  [^String text m]
  (let [builder (StringBuilder.)]
    (loop [text text]
      (cond
        (zero? (count text))
        (.toString builder)

        (.startsWith text "{")
        (let [brace (.indexOf text "}")]
          (if (neg? brace)
            (.toString (.append builder text))
            (do
              (.append builder (get m (keyword (subs text 1 brace))))
              (recur (subs text (inc brace))))))

        :else
        (let [brace (.indexOf text "{")]
          (if (neg? brace)
            (.toString (.append builder text))
            (do
              (.append builder (subs text 0 brace))
              (recur (subs text brace)))))))))

It passes all tests, so it should work.

UPDATE: Support non-key brace enclosed values ("this is a {not-a-key-{foo}-in-the-map} test" => "this is a {not-a-key-FOO-in-the-map} test"), allowing it to be used in a Java code generator where non-key brace-enclosed things are significant :-).

(defn replace-templates-even-newer
  "Return a String with each occurrence of a substring of the form {key}
   replaced with the corresponding value from a map parameter.
   @param str the String in which to do the replacements
   @param m a map of keyword->value
   @thanks kotarak http://stackoverflow.com/questions/6112534/
     follow-up-to-simple-string-template-replacement-in-scala-and-clojure"
  [^String text m]
  (let [builder (StringBuilder.)]
    (loop [text text]
      (cond
        (zero? (count text))
        (.toString builder)

        (.startsWith text "{")
        (let [brace (.indexOf text "}")]
          (if (neg? brace)
            (.toString (.append builder text))
            (if-let [[_ replacement] (find m (keyword (subs text 1 brace)))]
              (do
                (.append builder replacement)
                (recur (subs text (inc brace))))
              (do
                (.append builder "{")
                (recur (subs text 1))))))

        :else
        (let [brace (.indexOf text "{")]
          (if (neg? brace)
            (.toString (.append builder text))
            (do
              (.append builder (subs text 0 brace))
              (recur (subs text brace)))))))))