Implement Object.getNotifier() and remove Object.notify()

src/object-observe.js

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 16 matching lines @@
 
 "use strict";
 
 var InternalObjectIsFrozen = $Object.isFrozen;
 var InternalObjectFreeze = $Object.freeze;
 
 var observationState = %GetObservationState();
 if (IS_UNDEFINED(observationState.observerInfoMap)) {
   observationState.observerInfoMap = %CreateObjectHashTable();
   observationState.objectInfoMap = %CreateObjectHashTable();
+  observationState.notifierTargetMap = %CreateObjectHashTable();
   observationState.activeObservers = new InternalArray;
   observationState.observerPriority = 0;
 }
 
 function InternalObjectHashTable(tableName) {
   this.tableName = tableName;
 }
 
 InternalObjectHashTable.prototype = {
   get: function(key) {
     return %ObjectHashTableGet(observationState[this.tableName], key);
   },
   set: function(key, value) {
     observationState[this.tableName] =
         %ObjectHashTableSet(observationState[this.tableName], key, value);
   },
   has: function(key) {
     return %ObjectHashTableHas(observationState[this.tableName], key);
   }
 };
 
 var observerInfoMap = new InternalObjectHashTable('observerInfoMap');
 var objectInfoMap = new InternalObjectHashTable('objectInfoMap');
+var notifierTargetMap = new InternalObjectHashTable('notifierTargetMap');
+
+function CreateObjectInfo(object) {
+  var info = {
+    changeObservers: new InternalArray,

[rossberg, 2012/11/09 14:41:25]

Nit: can we perhaps rename that property to just "observers"? Sounds less like a
method. :)

[adamk, 2012/11/09 14:48:41]

It's named like this to match the spec's [[ChangeObservers]]; Rafael, ok with
you if we change this to not match?

+    notifier: null,
+  };
+  objectInfoMap.set(object, info);
+  return info;
+}
 
 function ObjectObserve(object, callback) {
   if (!IS_SPEC_OBJECT(object))
     throw MakeTypeError("observe_non_object", ["observe"]);
   if (!IS_SPEC_FUNCTION(callback))
     throw MakeTypeError("observe_non_function", ["observe"]);
   if (InternalObjectIsFrozen(callback))
     throw MakeTypeError("observe_callback_frozen");
 
   if (!observerInfoMap.has(callback)) {
     observerInfoMap.set(callback, {
       pendingChangeRecords: null,
       priority: observationState.observerPriority++,
     });
   }
 
   var objectInfo = objectInfoMap.get(object);
   if (IS_UNDEFINED(objectInfo)) {
-    // TODO: setup objectInfo.notifier
-    objectInfo = {
-      changeObservers: new InternalArray(callback)
-    };
-    objectInfoMap.set(object, objectInfo);
+    objectInfo = CreateObjectInfo(object);
     %SetIsObserved(object, true);
-    return;
   }
 
   var changeObservers = objectInfo.changeObservers;
   if (changeObservers.indexOf(callback) >= 0)
     return;
 
   changeObservers.push(callback);
 }
 
 function ObjectUnobserve(object, callback) {
@@ skipping 28 matching lines @@
 
 function NotifyChange(type, object, name, oldValue) {
   var objectInfo = objectInfoMap.get(object);
   var changeRecord = (arguments.length < 4) ?
       { type: type, object: object, name: name } :
       { type: type, object: object, name: name, oldValue: oldValue };
   InternalObjectFreeze(changeRecord);
   EnqueueChangeRecord(changeRecord, objectInfo.changeObservers);
 }
 
-function ObjectNotify(object, changeRecord) {
-  // TODO: notifier needs to be [[THIS]]
+var notifierPrototype = {};
+
+function ObjectNotifierNotify(changeRecord) {
+  if (IS_NULL_OR_UNDEFINED(this) && !IS_UNDETECTABLE(this))
+    throw MakeTypeError("called_on_null_or_undefined", ["notify"]);
+
+  var target = notifierTargetMap.get(this);
+  if (IS_UNDEFINED(target))
+    return;

[rossberg, 2012/11/09 14:41:25]

This is calling the notify method on something that's not a notifier. Shouldn't
this better be an error?

[adamk, 2012/11/09 14:48:41]

Here's what arv said about this when I asked him a few months ago:
"""
No, we are trying to remove nominal typing from ES6.
In this case I have considered adding these internal properties lazily
as needed. This might be required to allow a proxy to be used as a
notifier.
"""

[rossberg, 2012/11/09 15:06:17]

Hm, I don't buy that -- I think "nominal typing" is a red herring here.
Logically, 'target' is best viewed as being a private property of the notifier
(you could actually implement it that way using ES6 private names, if we had
them already). From that POV, it's also natural to throw if the property doesn't
exist on 'this'.

[arv (Not doing code reviews), 2012/11/09 15:22:22]

I don't remember my logic.
I agree. This is similar to how Map and Set are specified. If the internal
property does not exist it should throw.

+
   if (!IS_STRING(changeRecord.type))
     throw MakeTypeError("observe_type_non_string");
 
-  var objectInfo = objectInfoMap.get(object);
+  var objectInfo = objectInfoMap.get(target);
   if (IS_UNDEFINED(objectInfo))
     return;
 
+  if (!objectInfo.changeObservers.length)
+    return;
+
   var newRecord = {
-    object: object  // TODO: Needs to be 'object' retrieved from notifier
+    object: target
   };
   for (var prop in changeRecord) {
     if (prop === 'object')
       continue;
     newRecord[prop] = changeRecord[prop];
   }
   InternalObjectFreeze(newRecord);
 
   EnqueueChangeRecord(newRecord, objectInfo.changeObservers);
 }
 
+function ObjectGetNotifier(object) {
+  if (!IS_SPEC_OBJECT(object))
+    throw MakeTypeError("observe_non_object", ["getNotifier"]);
+
+  if (InternalObjectIsFrozen(object))
+    return null;
+
+  var objectInfo = objectInfoMap.get(object);
+  if (IS_UNDEFINED(objectInfo))
+    objectInfo = CreateObjectInfo(object);
+
+  if (IS_NULL(objectInfo.notifier)) {
+    objectInfo.notifier = {
+      __proto__: notifierPrototype
+    };
+    notifierTargetMap.set(objectInfo.notifier, object);
+  }
+
+  return objectInfo.notifier;
+}
+
 function DeliverChangeRecordsForObserver(observer) {
   var observerInfo = observerInfoMap.get(observer);
   if (IS_UNDEFINED(observerInfo))
     return;
 
   var pendingChangeRecords = observerInfo.pendingChangeRecords;
   if (IS_NULL(pendingChangeRecords))
     return;
 
   observerInfo.pendingChangeRecords = null;
@@ skipping 18 matching lines @@
     for (var i in activeObservers) {
       DeliverChangeRecordsForObserver(activeObservers[i]);
     }
   }
 }
 
 function SetupObjectObserve() {
   %CheckIsBootstrapping();
   InstallFunctions($Object, DONT_ENUM, $Array(
     "deliverChangeRecords", ObjectDeliverChangeRecords,
-    "notify", ObjectNotify,  // TODO: Remove when getNotifier is implemented.
+    "getNotifier", ObjectGetNotifier,
     "observe", ObjectObserve,
     "unobserve", ObjectUnobserve
   ));
+  InstallFunctions(notifierPrototype, DONT_ENUM, $Array(
+    "notify", ObjectNotifierNotify
+  ));
 }
 
 SetupObjectObserve();