Significant performance improvements

 * utils/clone uses a for-in loop instead of mapping over Object.keys.
 * State.prototype.clone, State.prototype.set, and State.prototype.get no
   longer perform unnecessary clones.

lib/State.js

@@ -39,7 +39,7 @@ var State = function () {
   _createClass(State, [{
     key: 'clone',
     value: function clone() {
-      return new State(this.toObject());
+      return new State(this.obj);
     }
   }, {
     key: 'toObject',
@@ -49,18 +49,22 @@ var State = function () {
   }, {
     key: 'set',
     value: function set(prop, val) {
-      var obj = this.toObject();
+      var newObj = {};
 
-      obj[prop] = val;
+      newObj[prop] = val;
 
-      return new State(obj);
+      return new State(Object.assign({}, this.obj, newObj));
     }
   }, {
     key: 'get',
     value: function get(prop) {
-      var obj = this.toObject();
+      var val = this.obj[prop];
+
+      if ((typeof val === 'undefined' ? 'undefined' : _typeof(val)) === 'object' && !val.hasOwnProperty('@@Plait/State')) {
+        return (0, _clone2.default)(val);
+      }
 
-      return obj[prop];
+      return val;
     }
   }, {
     key: 'update',

lib/utils/clone.js

@@ -10,7 +10,7 @@ exports.default = clone;
 function clone(obj) {
   var newObj = Array.isArray(obj) ? [] : {};
 
-  Object.keys(obj).map(function (k) {
+  for (var k in obj) {
     var val = obj[k];
 
     if ((typeof val === 'undefined' ? 'undefined' : _typeof(val)) === 'object') {
@@ -22,7 +22,7 @@ function clone(obj) {
     } else {
       newObj[k] = val;
     }
-  });
+  }
 
   return newObj;
 }

src/State.js

@@ -14,25 +14,29 @@ class State {
   }
 
   clone () {
-    return new State(this.toObject())
+    return new State(this.obj)
   }
 
   toObject () {
     return clone(this.obj)
   }
 
   set (prop, val) {
-    const obj = this.toObject()
+    const newObj = {}
 
-    obj[prop] = val
+    newObj[prop] = val
 
-    return new State(obj)
+    return new State(Object.assign({}, this.obj, newObj))
   }
 
   get (prop) {
-    const obj = this.toObject()
+    const val = this.obj[prop]
+
+    if (typeof val === 'object' && !val.hasOwnProperty('@@Plait/State')) {
+      return clone(val)
+    }
 
-    return obj[prop]
+    return val
   }
 
   update (prop, updater) {

src/utils/clone.js

@@ -1,7 +1,7 @@
 export default function clone (obj) {
   const newObj = Array.isArray(obj) ? [] : {}
 
-  Object.keys(obj).map(k => {
+  for (const k in obj) {
     const val = obj[k]
 
     if (typeof val === 'object') {
@@ -13,7 +13,7 @@ export default function clone (obj) {
     } else {
       newObj[k] = val
     }
-  })
+  }
 
   return newObj
 }

test/StateSpec.js

@@ -24,12 +24,15 @@ describe('State', () => {
   })
 
   it('is actually immutable', () => {
-    const obj = { a: 1 }
+    const nestedObj = { a: { nested: 1 } }
+    const obj = { a: 1, deep: nestedObj }
     const state = new State(obj)
 
     obj.a = 2
+    state.get('deep').a.nested = 2
 
     expect(state.get('a')).toBe(1)
+    expect(state.get('deep').a.nested).toBe(1)
   })
 
   it('is deeply immutable', () => {