Creates a mapping from elements to their associated ui objects.

@param <T> the type that the element is mapped to

class ElementMapperImpl<T extends UiObject> {

 static const String UI_OBJECT_ID = "uiObjectID";

 static void clearIndex(dart_html.Element elem) {
   assert(elem != null);
   elem.dataset.remove(UI_OBJECT_ID);
 }

 static int getIndex(dart_html.Element elem) {
   assert(elem != null);
   if (elem.dataset.containsKey(UI_OBJECT_ID)) { 
     return int.parse(elem.dataset[UI_OBJECT_ID]);
   } else {
     return -1;
   }
 }

 static void setIndex(dart_html.Element elem, int index) {
   assert(elem != null);
   assert(index != null);
   assert(index >= 0);
   elem.dataset[UI_OBJECT_ID] = index.toString();
 }

 FreeNode freeList = null;

 final List<T> uiObjectList = new List<T>();

 /**
  * Returns the uiObject associated with the given element.
  *
  * @param elem uiObject's element
  * @return the uiObject
  */
 T get(dart_html.Element elem) {
   int index = getIndex(elem);
   if (index < 0) {
     return null;
   }
   return uiObjectList[index];
 }

 /**
  * Gets the list of ui objects contained in this element mapper.
  *
  * @return the list of ui objects
  */
 List<T> getObjectList() {
   return uiObjectList;
 }

 /**
  * Creates an iterator from the ui objects stored within.
  *
  * @return an iterator of the ui objects indexed by this element mapper.
  */
 Iterator<T> iterator() {
   return uiObjectList.iterator;
 }

 /**
  * Adds the MappedType.
  *
  * @param uiObject uiObject to add
  */
 void put(T uiObject) {
   int index;
   if (freeList == null) {
     index = uiObjectList.length;
     uiObjectList.add(uiObject);
   } else {
     index = freeList.index;
     uiObjectList[index] = uiObject;
     freeList = freeList.next;
   }
   setIndex(uiObject.getElement(), index);
 }

 /**
  * Remove the uiObject associated with the given element.
  *
  * @param elem the uiObject's element
  */
 void removeByElement(dart_html.Element elem) {
   int index = getIndex(elem);
   removeImpl(elem, index);
 }

 void removeImpl(dart_html.Element elem, int index) {
   clearIndex(elem);
   uiObjectList[index] = null;
   freeList = new FreeNode(index, freeList);
 }
}