Error when assigning to Result index or length

Added some tests. Turns out our Chrome layer already did this too, so no changes were needed there.

Resolves #70

src/RJSResults.mm

@@ -52,6 +52,27 @@ JSValueRef ResultsGetProperty(JSContextRef ctx, JSObjectRef object, JSStringRef
     }
 }
 
+bool ResultsSetProperty(JSContextRef ctx, JSObjectRef object, JSStringRef propertyName, JSValueRef value, JSValueRef *jsException) {
+    try {
+        std::string indexStr = RJSStringForJSString(propertyName);
+        if (indexStr != "length") {
+            std::stol(RJSStringForJSString(propertyName));
+        }
+
+        // attempts to assign to 'length' or an index should throw an exception
+        throw std::runtime_error("Results objects are readonly");
+    }
+    catch (std::invalid_argument &exp) {
+        // for stol failure this could be another property that is handled externally, so ignore
+    }
+    catch (std::exception &exp) {
+        if (jsException) {
+            *jsException = RJSMakeError(ctx, exp);
+        }
+    }
+    return false;
+}
+
 void ResultsPropertyNames(JSContextRef ctx, JSObjectRef object, JSPropertyNameAccumulatorRef propertyNames) {
     Results *results = RJSGetInternal<Results *>(object);
     char str[32];
@@ -124,6 +145,6 @@ static const JSStaticFunction RJSResultsFuncs[] = {
 };
 
 JSClassRef RJSResultsClass() {
-    static JSClassRef s_objectClass = RJSCreateWrapperClass<Results *>("Results", ResultsGetProperty, NULL, RJSResultsFuncs, ResultsPropertyNames);
+    static JSClassRef s_objectClass = RJSCreateWrapperClass<Results *>("Results", ResultsGetProperty, ResultsSetProperty, RJSResultsFuncs, ResultsPropertyNames);
     return s_objectClass;
 }

tests/ResultsTests.js

@@ -50,6 +50,27 @@ module.exports = BaseTest.extend({
         TestCase.assertTrue(Object.getPrototypeOf(people[0]) === schemas.PersonObject.prototype);
         TestCase.assertTrue(people[0] instanceof schemas.PersonObject);
     },
+    testResultsReadonly: function() {
+        var realm = new Realm({schema: [schemas.TestObject]});
+        var objects = realm.objects('TestObject');
+
+        realm.write(function() {
+            realm.create('TestObject', [1]);
+        });
+
+        TestCase.assertThrows(function() {
+            objects[-1] = [0];
+        });
+        TestCase.assertThrows(function() {
+            objects[0] = [0];
+        });
+        TestCase.assertThrows(function() {
+            objects[1] = [0];
+        });
+        TestCase.assertThrows(function() {
+            objects.length = 0;
+        });
+    },
     testResultsInvalidProperty: function() {
         var realm = new Realm({schema: [schemas.TestObject]});
         var objects = realm.objects('TestObject');