Add update

src/plumbing/core.clj

@@ -30,6 +30,16 @@
             (reset! m-atom# (assoc! ~m-sym ~key-expr ~val-expr))))
         (persistent! @m-atom#))))
 
+(defn update
+  "Updates the value in map m at k with the function f.
+
+  Like update-in, but for updating a single top-level key.
+  Any additional args will be passed to f after the value."
+  ([m k f] (assoc m k (f (get m k))))
+  ([m k f x1] (assoc m k (f (get m k) x1)))
+  ([m k f x1 x2] (assoc m k (f (get m k) x1 x2)))
+  ([m k f x1 x2 & xs] (assoc m k (apply f (get m k) x1 x2 xs))))
+
 (defn map-vals
   "Build map k -> (f v) for [k v] in map, preserving the initial type"
   [f m]

test/plumbing/core_test.clj

@@ -27,6 +27,20 @@
     (is (= (count m) 1000))
     (is (= (m 999) 499500))))
 
+(deftest update-test
+  (testing "0 extra args"
+    (is (= {:a 5, :b 0}
+           (update {:a 4, :b 0} :a inc)))
+    (is (= {:a 1}
+           (update {} :a (fnil inc 0)))))
+  (testing "1 extra arg"
+    (is (= {:a 42, :b 0}
+           (update {:a 6, :b 0} :a * 7)))
+    (is (= {:a #{42}}
+           (update {} :a (fnil conj #{}) 42))))
+  (testing "100 extra args"
+    (is (= {:a 4951} (apply update {:a 1} :a + (range 100))))))
+
 (deftest map-vals-test
   (is (= (map-vals inc {:a 0 :b 0})
          {:a 1 :b 1}))