[new] Add merge-nx

taoensso · Oct 30, 2024 · dc06199 · dc06199
1 parent e2cae57
commit dc06199
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Showing 2 changed files with 25 additions and 8 deletions.
diff --git a/src/taoensso/encore.cljc b/src/taoensso/encore.cljc
@@ -2821,8 +2821,8 @@
 
 (defn merge
   "Like `core/merge` but:
-    - Often faster, with much better worst-case performance.
-    - Supports `:merge/dissoc` vals."
+    - Supports `:merge/dissoc` vals.
+    - Often faster, with much better worst-case performance."
   ([               ] nil)
   ([m1             ] (p! m1))
   ([m1 m2          ] (p!                                                     (merge-with* false nil m1 m2)))
@@ -2831,9 +2831,9 @@
 
 (defn nested-merge
   "Like `core/merge` but:
-    - Often faster, with much better worst-case performance.
+    - Recursively merges nested maps.
     - Supports `:merge/dissoc` vals.
-    - Recursively merges nested maps."
+    - Often faster, with much better worst-case performance."
   ([               ] nil)
   ([m1             ] (p! m1))
   ([m1 m2          ] (p!                                                   (merge-with* true nil m1 m2)))
@@ -2842,8 +2842,8 @@
 
 (defn merge-with
   "Like `core/merge-with` but:
-    - Often faster, with much better worst-case performance.
-    - Supports `:merge/dissoc` vals."
+    - Supports `:merge/dissoc` vals.
+    - Often faster, with much better worst-case performance."
   ([f                ] nil)
   ([f m1             ] (p! m1))
   ([f m1 m2          ] (p!                                                 (merge-with* false f m1 m2)))
@@ -2852,15 +2852,27 @@
 
 (defn nested-merge-with
   "Like `core/merge-with` but:
-    - Often faster, with much better worst-case performance.
+    - Recursively merges nested maps.
     - Supports `:merge/dissoc` vals.
-    - Recursively merges nested maps."
+    - Often faster, with much better worst-case performance."
   ([f                ] nil)
   ([f m1             ] (p! m1))
   ([f m1 m2          ] (p!                                               (merge-with* true f m1 m2)))
   ([f m1 m2 m3       ] (p!                           (merge-with* true f (merge-with* true f m1 m2) m3)))
   ([f m1 m2 m3 & more] (p! (merge-with* true f (cons (merge-with* true f (merge-with* true f m1 m2) m3) more)))))
 
+(let [mf (fn [x y] x)]
+  (defn merge-nx
+    "Like `core/merge` but:
+      - Preserves existing values (so useful for merging defaults).
+      - Supports `:merge/dissoc` vals.
+      - Often faster, with much better worst-case performance."
+    ([               ] nil)
+    ([m1             ] (p! m1))
+    ([m1 m2          ] (p!                                                   (merge-with* false mf m1 m2)))
+    ([m1 m2 m3       ] (p!                             (merge-with* false mf (merge-with* false mf m1 m2) m3)))
+    ([m1 m2 m3 & more] (p! (merge-with* false mf (cons (merge-with* false mf (merge-with* false mf m1 m2) m3) more))))))
+
 (comment
   (qb 1e6 ; [182.63 122.16 167.18]
     (core-merge   {:a 1} {:a {:b 1}} {:a {:c 1}})

diff --git a/test/taoensso/encore_tests.cljc b/test/taoensso/encore_tests.cljc
@@ -502,6 +502,11 @@
 
       (is (= (enc/merge {:a 1} {:b 2} {:a 3} {:c 4}) {:a 3, :b 2, :c 4}))])
 
+   (testing "nx (preserve existing)"
+     [(is (= (enc/merge-nx {:a 1} {:a 2 :b 2}) {:a 1, :b 2}))
+      (is (= (enc/merge-nx {}     {:a 2 :b 2}) {:a 2, :b 2}))
+      (is (= (enc/merge-nx {} {:a 2} {:a 3} {:b 4} {:a 5} {:c 6}) {:a 2, :b 4, :c 6}))])
+
    (testing "Transient support (currently undocumented)"
      [(is (= (enc/merge (transient {})) {}))
       (is (= (enc/merge nil (transient {})) nil))