redplanetlabs#223 - Improve before-index performance

Adding before-index implementation that uses take/drop instead of setval/srange

Adding new functional test to confirm behavior when operating on a string

Adding benchmark for old versus new implementation of before-index

scripts/benchmarks.clj

@@ -335,3 +335,9 @@
     (transform (walker number?) inc data)
     (transform (walker-old number?) inc data)
     ))
+
+(let [data (vec (range 1000)) insert-idx 500]
+  (run-benchmark "old versus new before-index implementation"
+    (setval (before-index-old insert-idx) -1 data)
+    (setval (before-index-new insert-idx) -1 data)
+    ))

src/clj/com/rpl/specter.cljc

@@ -968,7 +968,7 @@
 (defrichnav
   ^{:doc "Navigates to the empty space between the index and the prior index. For select
           navigates to NONE, and transforms to non-NONE insert at that position."}
-  before-index
+  before-index-old
   [index]
   (select* [this vals structure next-fn]
     NONE)
@@ -980,6 +980,28 @@
         (setval (srange index index) [v] structure)
         ))))
 
+(defrichnav
+  ^{:doc "Navigates to the empty space between the index and the prior index. For select
+          navigates to NONE, and transforms to non-NONE insert at that position."}
+  before-index-new
+  [index]
+  (select* [this vals structure next-fn]
+           NONE)
+  (transform* [this vals structure next-fn]
+              (let [v (next-fn vals NONE)]
+                (if (identical? NONE v)
+                  structure
+                  (let [updated (concat (take index structure) [v] (drop index structure))]
+                    (if (string? structure)
+                      (apply str updated)
+                      updated
+                    )
+                  )))))
+
+;; (temporarily) assign before-index-new to before-index so existing tests are exercised against it
+;; to be removed before a final merge (wherein before-index-new is also renamed to before-index)
+(def before-index before-index-new)
+
 (defrichnav
   ^{:doc "Navigates to the index of the sequence if within 0 and size. Transforms move element
           at that index to the new index, shifting other elements in the sequence."}

test/com/rpl/specter/core_test.cljc

@@ -1609,14 +1609,16 @@
 
 (deftest before-index-test
   (let [data [1 2 3]
-        datal '(1 2 3)]
+        datal '(1 2 3)
+        datastr "abcdef"]
     (is (predand= vector? [:a 1 2 3] (setval (s/before-index 0) :a data)))
     (is (predand= vector? [1 2 3] (setval (s/before-index 1) s/NONE data)))
     (is (predand= vector? [1 :a 2 3] (setval (s/before-index 1) :a data)))
     (is (predand= vector? [1 2 3 :a] (setval (s/before-index 3) :a data)))
     (is (predand= list? '(:a 1 2 3) (setval (s/before-index 0) :a datal)))
     (is (predand= list? '(1 :a 2 3) (setval (s/before-index 1) :a datal)))
     (is (predand= list? '(1 2 3 :a) (setval (s/before-index 3) :a datal)))
+    (is (predand= string? "abcxdef" (setval (s/before-index 3) (char \x) datastr)))
     ))
 
 (deftest index-nav-test