Make cursor more general and flexible

Instead of passing an atom, you can now pass a function.

That function is passed one argument (the path provided to cursor)
when deref-ing, and two arguments (path and new value) when
resetting.

Remove the old setter, and the currying version.

src/reagent/core.cljs

@@ -212,19 +212,11 @@ the specified path within the wrapped Reagent atom. e.g.,
     ... (reset! c 42) ;; equivalent to (swap! ra assoc-in [:nested :content] 42)
     ... (swap! c inc) ;; equivalence to (swap! ra update-in [:nested :content] inc)
     )
-The third argument may be a function, that is called with
-optional extra arguments provided to cursor, and the new value of the
-resulting 'atom'. If such a function is given, it should update the
-given Reagent atom.
 "
-  ([path] (fn [ra] (cursor path ra)))
   ([path ra]
-   (assert (satisfies? IDeref ra))
-   (ratom/cursor path ra))
-  ([path ra reset-fn & args]
-   (assert (satisfies? IDeref ra))
-   (assert (ifn? reset-fn))
-   (ratom/cursor path ra reset-fn args)))
+   (assert (or (satisfies? IDeref ra)
+               (ifn? ra)))
+   (ratom/cursor path ra)))
 
 ;; Utilities
 

src/reagent/ratom.cljs

@@ -105,13 +105,13 @@
   (_reaction [this]
     (if (nil? reaction)
       (set! reaction
-            (make-reaction
-             #(get-in @ratom path)
-             :on-set (if setf
-                       #(setf %2)
-                       (if (= path [])
-                         #(reset! ratom %2)
-                         #(swap! ratom assoc-in path %2)))))
+            (if (satisfies? IDeref ratom)
+              (make-reaction #(get-in @ratom path)
+                             :on-set (if (= path [])
+                                       #(reset! ratom %2)
+                                       #(swap! ratom assoc-in path %2)))
+              (make-reaction #(ratom path)
+                             :on-set #(ratom path %2))))
       reaction))
 
   (_peek [this]

test/testcursor.cljs

@@ -262,18 +262,27 @@
   (let [a (atom {:foo "bar"})
         a1 (atom {:foo "bar"})
         c (r/cursor [:foo] a)
-        c2 (r/cursor [:foo] a swap! a assoc :foo)
-        c3 (r/cursor [:foo] a swap! a assoc :foobar)]
+        foo (fn
+              ([path] (get-in @a path))
+              ([path v] (swap! a assoc-in path v)))
+        foobar (fn
+                 ([path] (get-in @a path))
+                 ([path v] (swap! a assoc :foobar v)))
+        c2 (r/cursor [:foo] foo)
+        c3 (r/cursor [:foo] foobar)]
+
     (is (= @c "bar"))
     (is (= @c2 "bar"))
     (is (= @c3 "bar"))
     (is (= c (r/cursor [:foo] a)))
     (is (not= c (r/cursor [:foo] a1)))
     (is (not= c (r/cursor [:foobar] a)))
-    (is (= c2 (r/cursor [:foo] a swap! a assoc :foo)))
-    (is (not= c2 (r/cursor [:foo] a swap! a assoc :foobar)))
-    (is (not= c2 (r/cursor [:foo] a1 swap! a assoc :foo)))
-    (is (not= c2 (r/cursor [:foo] a swap! a1 assoc :foo)))
+    (is (= c2 (r/cursor [:foo] foo)))
+    (is (= c3 (r/cursor [:foo] foobar)))
+    (is (= c2 c2))
+    (is (not= c2 (r/cursor [:foo] foobar)))
+    (is (not= c3 (r/cursor [:foo] foo)))
+    (is (not= c2 (r/cursor [:foobar] foo)))
 
     (reset! c2 "foobar")
     (is (= @c2 "foobar"))
@@ -285,7 +294,7 @@
     (is (= @c "bar"))
     (is (= @a {:foo "bar"}))
     (is (= c (r/cursor [:foo] a)))
-    (is (= c2 (r/cursor [:foo] a swap! a assoc :foo)))
+    (is (= c2 (r/cursor [:foo] foo)))
 
     (reset! c3 "foo")
     (is (= @a {:foo "bar" :foobar "foo"}))))