Add update and updateIn functions

README.md

@@ -199,6 +199,34 @@ Immutable({type: {main: "parrot", sub: "Norwegian Blue"}, status: "alive"}).setI
 // returns Immutable({type: {main: "parrot", sub: "Norwegian Ridgeback"}, status: "alive"})
 ```
 
+### update
+
+Returns an Immutable Object with a single property updated using the provided updater function.
+
+```javascript
+function inc (x) { return x + 1 }
+Immutable({foo: 1}).update("foo", inc)
+// returns Immutable({foo: 2})
+```
+
+All additional arguments will be passed to the updater function.
+
+```javascript
+function add (x, y) { return x + y }
+Immutable({foo: 1}).update("foo", add, 10)
+// returns Immutable({foo: 11})
+```
+
+### updateIn
+
+Like [update](#update), but accepts a nested path to the property.
+
+```javascript
+function add (x, y) { return x + y }
+Immutable({foo: {bar: 1}}).updateIn(["foo", "bar"], add, 10)
+// returns Immutable({foo: {bar: 11}})
+```
+
 ### without
 
 ```javascript

seamless-immutable.development.js

@@ -151,6 +151,8 @@
     addPropertyTo(array, "asMutable", asMutableArray);
     addPropertyTo(array, "set", arraySet);
     addPropertyTo(array, "setIn", arraySetIn);
+    addPropertyTo(array, "update", update);
+    addPropertyTo(array, "updateIn", updateIn);
 
     for(var i = 0, length = array.length; i < length; i++) {
       array[i] = Immutable(array[i]);
@@ -430,6 +432,28 @@
     return makeImmutableObject(mutable, this);
   }
 
+  function update(property, updater) {
+    var restArgs = Array.prototype.slice.call(arguments, 2);
+    var initialVal = this[property];
+    return this.set(property, updater.apply(initialVal, [initialVal].concat(restArgs)));
+  }
+
+  function getInPath(obj, path) {
+    /*jshint eqnull:true */
+    for (var i = 0, l = path.length; obj != null && i < l; i++) {
+      obj = obj[path[i]];
+    }
+
+    return (i && i == l) ? obj : undefined;
+  }
+
+  function updateIn(path, updater) {
+    var restArgs = Array.prototype.slice.call(arguments, 2);
+    var initialVal = getInPath(this, path);
+
+    return this.setIn(path, updater.apply(initialVal, [initialVal].concat(restArgs)));
+  }
+
   function asMutableObject(opts) {
     var result = this.instantiateEmptyObject(), key;
 
@@ -467,6 +491,8 @@
     addPropertyTo(obj, "instantiateEmptyObject", instantiateEmptyObject);
     addPropertyTo(obj, "set", objectSet);
     addPropertyTo(obj, "setIn", objectSetIn);
+    addPropertyTo(obj, "update", update);
+    addPropertyTo(obj, "updateIn", updateIn);
 
     return makeImmutable(obj, mutatingObjectMethods);
   }