Various udpates.

src/MappedCollection2.coffee

@@ -186,7 +186,7 @@ class $MappedCollection2 extends $EventEmitter
       key: rule.key() # No context because there is not generator.
       val: undefined
     }
-    @_updateItems [item]
+    @_updateItems [item], true
 
   # Register a new rule.
   #

src/helpers.coffee

@@ -76,6 +76,17 @@ $watch = (collection, {
 
   # Initial value.
   init
+
+  # Function called when a loop is detected.
+  #
+  # Usually it is used to either throw an exception or do nothing to
+  # stop the loop.
+  #
+  # Note: The function may also returns `true` to force the processing
+  # to continue.
+  #
+  # Default: -> throw new Error 'loop detected'
+  loopDetected
 }, fn) ->
   val = if val is undefined
     # The default value is simply the value of the item.
@@ -83,6 +94,8 @@ $watch = (collection, {
   else
     $asFunction val
 
+  loopDetected ?= -> throw new Error 'loop detected'
+
   # Method allowing the cleanup when the helper is no longer used.
   #cleanUp = -> # TODO: noop for now.
 
@@ -99,7 +112,7 @@ $watch = (collection, {
     # Values are grouped by namespace.
     valuesByNamespace = Object.create null
 
-    $each items, (item) ->
+    $each items, (item, key) -> # `key` is a local variable.
       return unless not cond? or cond.call item
 
       if bind?
@@ -122,7 +135,8 @@ $watch = (collection, {
       return false for _ of valuesByNamespace
       true
 
-    throw new Error 'loop detected' if isProcessing
+    if isProcessing
+      return unless loopDetected() is true
     isProcessing = true
 
     # For each namespace.
@@ -189,18 +203,26 @@ $watch = (collection, {
 
   # Creates the generator: the function which items will used to
   # register to this watcher and to get the current value.
-  generator = ->
-    {key} = this
+  generator = do (key) -> # Declare a local variable.
+    ->
+      {key} = this
 
-    # Register this item has a consumer.
-    consumers[@key] = true
+      # Register this item has a consumer.
+      consumers[key] = true
 
-    # Returns the value for this item if any or the common value.
-    namespace = "$#{key}"
-    if namespace of values
-      values[namespace]
-    else
-      values.common
+      # Returns the value for this item if any or the common value.
+      namespace = "$#{key}"
+      if namespace of values
+        values[namespace]
+      else
+        values.common
+
+  # Creates a helper to unregister an item from this watcher.
+  generator.unregister = do (key) -> # Declare a local variable.
+    ->
+      {key} = this
+      delete consumers[key]
+      delete values["$#{key}"]
 
   # Creates a helper to get the value without using an item.
   generator.raw = (key) ->

src/spec2.coffee

@@ -87,7 +87,7 @@ module.exports = ->
     @rule rule, definition for rule in rules
 
   UUIDsToKeys = $map {
-    if: -> @val and 'UUID' of @val
+    if: -> 'UUID' of @val
     val: -> [@val.UUID, @key]
   }
 
@@ -527,8 +527,18 @@ module.exports = ->
       # TODO: UNIX timestamp?
       time: -> @genval.timestamp
 
-      # FIXME: loop
-      #object: -> (UUIDsToKeys.call this)[@genval.obj_uuid]
+      object: ->
+        # If the key of the concerned object has already be resolved
+        # returns the known value.
+        return @val.object if @val.object?
+
+        # Tries to resolve the key of the concerned object.
+        object = (UUIDsToKeys.call this)[@genval.obj_uuid]
+
+        # If resolved, unregister from the watcher.
+        UUIDsToKeys.unregister.call this if object?
+
+        object
 
       # TODO: Are these names meaningful?
       name: -> @genval.name