Optimize ngRepeat by using the new CD

lib/core/parser/syntax.dart

@@ -28,8 +28,8 @@ abstract class Visitor {
   visitPrefix(Prefix expression) => visitExpression(expression);
 
   visitLiteral(Literal expression) => visitExpression(expression);
-  visitLiteralPrimitive(LiteralPrimitive expression)
-      => visitLiteral(expression);
+  visitLiteralPrimitive(LiteralPrimitive expression) =>
+      visitLiteral(expression);
   visitLiteralString(LiteralString expression) => visitLiteral(expression);
   visitLiteralArray(LiteralArray expression) => visitLiteral(expression);
   visitLiteralObject(LiteralObject expression) => visitLiteral(expression);
@@ -39,12 +39,12 @@ abstract class Expression {
   bool get isAssignable => false;
   bool get isChain => false;
 
-  eval(scope, [FilterMap filters = defaultFilterMap])
-      => throw new EvalError("Cannot evaluate $this");
-  assign(scope, value)
-      => throw new EvalError("Cannot assign to $this");
-  bind(context, [LocalsWrapper wrapper])
-      => new BoundExpression(this, context, wrapper);
+  eval(scope, [FilterMap filters = defaultFilterMap]) =>
+      throw new EvalError("Cannot evaluate $this");
+  assign(scope, value) =>
+      throw new EvalError("Cannot assign to $this");
+  bind(context, [LocalsWrapper wrapper]) =>
+      new BoundExpression(this, context, wrapper);
 
   accept(Visitor visitor);
   String toString() => Unparser.unparse(this);

lib/core_dom/view.dart

@@ -29,7 +29,7 @@ class View {
 class ViewPort {
   final dom.Node placeholder;
   final NgAnimate _animate;
-  final List<View> _views = <View>[];
+  final _views = <View>[];
 
   ViewPort(this.placeholder, this._animate);
 
@@ -56,12 +56,12 @@ class ViewPort {
   }
 
   void _viewsInsertAfter(View view, View insertAfter) {
-    int index = (insertAfter != null) ? _views.indexOf(insertAfter) : -1;
-    _views.insert(index + 1, view);
+    int index = insertAfter == null ? 0 : _views.indexOf(insertAfter) + 1;
+    _views.insert(index, view);
   }
 
   dom.Node _lastNode(View insertAfter) =>
     insertAfter == null
       ? placeholder
-      : insertAfter.nodes[insertAfter.nodes.length - 1];
+      : insertAfter.nodes.last;
 }

lib/directive/ng_repeat.dart

@@ -1,16 +1,5 @@
 part of angular.directive;
 
-class _Row {
-  var id;
-  Scope scope;
-  View view;
-  dom.Element startNode;
-  dom.Element endNode;
-  List<dom.Element> nodes;
-
-  _Row(this.id);
-}
-
 /**
  * The `ngRepeat` directive instantiates a template once per item from a
  * collection. Each template instance gets its own scope, where the given loop
@@ -20,15 +9,15 @@ class _Row {
  * Special properties are exposed on the local scope of each template instance,
  * including:
  *
- * <table>
- * <tr><th> Variable  </th><th> Type </th><th> Details                                                                     <th></tr>
- * <tr><td> `$index`  </td><td>[num] </td><td> iterator offset of the repeated element (0..length-1)                       <td></tr>
- * <tr><td> `$first`  </td><td>[bool]</td><td> true if the repeated element is first in the iterator.                      <td></tr>
- * <tr><td> `$middle` </td><td>[bool]</td><td> true if the repeated element is between the first and last in the iterator. <td></tr>
- * <tr><td> `$last`   </td><td>[bool]</td><td> true if the repeated element is last in the iterator.                       <td></tr>
- * <tr><td> `$even`   </td><td>[bool]</td><td> true if the iterator position `$index` is even (otherwise false).           <td></tr>
- * <tr><td> `$odd`    </td><td>[bool]</td><td> true if the iterator position `$index` is odd (otherwise false).            <td></tr>
- * </table>
+ *   * `$index` ([:num:]) the iterator offset of the repeated element
+ *      (0..length-1)
+ *   * `$first`  ([:bool:]) whether the repeated element is first in the
+ *      iterator.
+ *   * `$middle` ([:bool:]) whether the repeated element is between the first
+ *      and last in the iterator.
+ *   * `$last` ([:bool:]) whether the repeated element is last in the iterator.
+ *   * `$even` ([:bool:]) whether the iterator position `$index` is even.
+ *   * `$odd` ([:bool:]) whether the iterator position `$index` is odd.
  *
  *
  * [repeat_expression] ngRepeat The expression indicating how to enumerate a
@@ -57,7 +46,7 @@ class _Row {
  *     function can be used to assign a unique `$$hashKey` property to each item
  *     in the array. This property is then used as a key to associated DOM
  *     elements with the corresponding item in the array by identity. Moving the
- *     same object in array would move the DOM element in the same way ian the
+ *     same object in array would move the DOM element in the same way in the
  *     DOM.
  *
  *     For example: `item in items track by item.id` is a typical pattern when
@@ -81,8 +70,8 @@ class _Row {
     selector: '[ng-repeat]',
     map: const {'.': '@expression'})
 class NgRepeatDirective {
-  static RegExp _SYNTAX = new RegExp(r'^\s*(.+)\s+in\s+(.*?)\s*(\s+track\s+by\s+(.+)\s*)?(\s+lazily\s*)?$');
-  static RegExp _LHS_SYNTAX = new RegExp(r'^(?:([\$\w]+)|\(([\$\w]+)\s*,\s*([\$\w]+)\))$');
+  static RegExp _SYNTAX = new RegExp(r'^\s*(.+)\s+in\s+(.*?)\s*(?:track\s+by\s+(.+)\s*)?(\s+lazily\s*)?$');
+  static RegExp _LHS_SYNTAX = new RegExp(r'^(?:([$\w]+)|\(([$\w]+)\s*,\s*([$\w]+)\))$');
 
   final ViewPort _viewPort;
   final BoundViewFactory _boundViewFactory;
@@ -95,156 +84,168 @@ class NgRepeatDirective {
   String _valueIdentifier;
   String _keyIdentifier;
   String _listExpr;
-  Map<dynamic, _Row> _rows = {};
-  Function _trackByIdFn = (key, value, index) => value;
-  Watch _watch = null;
-  Iterable _lastCollection;
+  List<_Row> _rows;
+  Function _generateId = (key, value, index) => value;
+  Watch _watch;
 
-  NgRepeatDirective(this._viewPort, this._boundViewFactory,
-                    this._scope, this._parser, this._astParser,
-                    this.filters);
+  NgRepeatDirective(this._viewPort, this._boundViewFactory, this._scope,
+                    this._parser, this._astParser, this.filters);
 
   set expression(value) {
     assert(value != null);
     _expression = value;
     if (_watch != null) _watch.remove();
+
     Match match = _SYNTAX.firstMatch(_expression);
     if (match == null) {
       throw "[NgErr7] ngRepeat error! Expected expression in form of '_item_ "
           "in _collection_[ track by _id_]' but got '$_expression'.";
     }
+
     _listExpr = match.group(2);
-    var trackByExpr = match.group(4);
+
+    var trackByExpr = match.group(3);
     if (trackByExpr != null) {
       Expression trackBy = _parser(trackByExpr);
-      _trackByIdFn = ((key, value, index) {
-        final trackByLocals = <String, Object>{};
-        if (_keyIdentifier != null) trackByLocals[_keyIdentifier] = key;
-        trackByLocals
+      _generateId = ((key, value, index) {
+        final context = <String, Object>{}
             ..[_valueIdentifier] = value
             ..[r'$index'] = index
             ..[r'$id'] = (obj) => obj;
-        return relaxFnArgs(trackBy.eval)(new ScopeLocals(_scope.context, trackByLocals));
+        if (_keyIdentifier != null) context[_keyIdentifier] = key;
+        return relaxFnArgs(trackBy.eval)(new ScopeLocals(_scope.context,
+            context));
       });
     }
+
     var assignExpr = match.group(1);
     match = _LHS_SYNTAX.firstMatch(assignExpr);
     if (match == null) {
       throw "[NgErr8] ngRepeat error! '_item_' in '_item_ in _collection_' "
           "should be an identifier or '(_key_, _value_)' expression, but got "
           "'$assignExpr'.";
     }
+
     _valueIdentifier = match.group(3);
     if (_valueIdentifier == null) _valueIdentifier = match.group(1);
     _keyIdentifier = match.group(2);
 
     _watch = _scope.watch(
         _astParser(_listExpr, collection: true, filters: filters),
-        (CollectionChangeRecord collection, _) {
-          //TODO(misko): we should take advantage of the CollectionChangeRecord!
-          _onCollectionChange(collection == null ? [] : collection.iterable);
+        (CollectionChangeRecord changes, _) {
+          if (changes is! CollectionChangeRecord) return;
+          _onChange(changes);
         }
     );
   }
 
-  List<_Row> _computeNewRows(Iterable collection, trackById) {
-    final newRowOrder = new List<_Row>(collection.length);
-    // Same as lastViewMap but it has the current state. It will become the
-    // lastViewMap on the next iteration.
-    final newRows = <dynamic, _Row>{};
-    // locate existing items
-    for (var index = 0; index < newRowOrder.length; index++) {
-      var value = collection.elementAt(index);
-      trackById = _trackByIdFn(index, value, index);
-      if (_rows.containsKey(trackById)) {
-        var row = _rows[trackById];
-        _rows.remove(trackById);
-        newRows[trackById] = row;
-        newRowOrder[index] = row;
-      } else if (newRows.containsKey(trackById)) {
-        // restore lastViewMap
-        newRowOrder.forEach((row) {
-          if (row != null && row.startNode != null) _rows[row.id] = row;
-        });
-        // This is a duplicate and we need to throw an error
-        throw "[NgErr50] ngRepeat error! Duplicates in a repeater are not "
-            "allowed. Use 'track by' expression to specify unique keys. "
-            "Repeater: $_expression, Duplicate key: $trackById";
-      } else {
-        // new never before seen row
-        newRowOrder[index] = new _Row(trackById);
-        newRows[trackById] = null;
+  // Computes and executes DOM changes when the item list changes
+  void _onChange(CollectionChangeRecord changes) {
+    final int length = changes.iterable.length;
+    final rows = new List<_Row>(length);
+    final changeFunctions = new List<Function>(length);
+    final removedIndexes = <int>[];
+    final int domLength = _rows == null ? 0 : _rows.length;
+    final leftInDom = new List.generate(domLength, (i) => domLength - 1 - i);
+    var domIndex;
+
+    var addRow = (int index, value, View previousView) {
+      var childContext = _updateContext(new PrototypeMap(_scope.context), index,
+          length)..[_valueIdentifier] = value;
+      var childScope = _scope.createChild(childContext);
+      var view = _boundViewFactory(childScope);
+      var nodes = view.nodes;
+      rows[index] = new _Row(_generateId(index, value, index))
+          ..view = view
+          ..scope = childScope
+          ..nodes = nodes
+          ..startNode = nodes.first
+          ..endNode = nodes.last;
+      _viewPort.insert(view, insertAfter: previousView);
+    };
+
+    if (_rows == null) {
+      _rows = new List<_Row>(length);
+      for (var i = 0; i < length; i++) {
+        changeFunctions[i] = (index, previousView) {
+          addRow(index, changes.iterable.elementAt(i), previousView);
+        };
       }
+    } else {
+      changes.forEachRemoval((removal) {
+        var index = removal.previousIndex;
+        var row = _rows[index];
+        row.scope.destroy();
+        _viewPort.remove(row.view);
+        leftInDom.removeAt(domLength - 1 - index);
+      });
+
+      changes.forEachAddition((addition) {
+        changeFunctions[addition.currentIndex] = (index, previousView) {
+          addRow(index, addition.item, previousView);
+        };
+      });
+
+      changes.forEachMove((move) {
+        var previousIndex = move.previousIndex;
+        var value = move.item;
+        changeFunctions[move.currentIndex] = (index, previousView) {
+          var previousRow = _rows[previousIndex];
+          var childScope = previousRow.scope;
+          var childContext = _updateContext(childScope.context, index, length);
+          if (!identical(childScope.context[_valueIdentifier], value)) {
+            childContext[_valueIdentifier] = value;
+          }
+          rows[index] = _rows[previousIndex];
+          // Only move the DOM node when required
+          if (domIndex < 0 || leftInDom[domIndex] != previousIndex) {
+            _viewPort.move(previousRow.view, moveAfter: previousView);
+            leftInDom.remove(previousIndex);
+          }
+          domIndex--;
+        };
+      });
     }
-    // remove existing items
-    _rows.forEach((key, row) {
-      _viewPort.remove(row.view);
-      row.scope.destroy();
-    });
-    _rows = newRows;
-    return newRowOrder;
-  }
 
-  _onCollectionChange(Iterable collection) {
-    dom.Node previousNode = _viewPort.placeholder; // current position of the
-    // node
-    dom.Node nextNode;
-    Scope childScope;
-    Map childContext;
-    Scope trackById;
-    View cursor;
-
-    List<_Row> newRowOrder = _computeNewRows(collection, trackById);
-
-    for (var index = 0; index < collection.length; index++) {
-      var value = collection.elementAt(index);
-      _Row row = newRowOrder[index];
-
-      if (row.startNode != null) {
-        // if we have already seen this object, then we need to reuse the
-        // associated scope/element
-        childScope = row.scope;
-        childContext = childScope.context as Map;
-
-        nextNode = previousNode;
-        do {
-          nextNode = nextNode.nextNode;
-        } while (nextNode != null);
-
-        if (row.startNode != nextNode) {
-          // existing item which got moved
-          _viewPort.move(row.view, moveAfter: cursor);
-        }
-        previousNode = row.endNode;
+    var previousView = null;
+    domIndex = leftInDom.length - 1;
+    for(var targetIndex = 0; targetIndex < length; targetIndex++) {
+      var changeFn = changeFunctions[targetIndex];
+      if (changeFn == null) {
+        rows[targetIndex] = _rows[targetIndex];
+        domIndex--;
+        // The element has not moved but `$last` and `$middle` might still need
+        // to be updated
+        _updateContext(rows[targetIndex].scope.context, targetIndex, length);
       } else {
-        // new item which we don't know about
-        childScope = _scope.createChild(childContext = new PrototypeMap(_scope.context));
-      }
-
-      if (!identical(childScope.context[_valueIdentifier], value)) {
-        childContext[_valueIdentifier] = value;
+        changeFn(targetIndex, previousView);
       }
-      var first = (index == 0);
-      var last = (index == collection.length - 1);
-      childContext
-          ..[r'$index'] = index
-          ..[r'$first'] = first
-          ..[r'$last'] = last
-          ..[r'$middle'] = !first && !last
-          ..[r'$odd'] = index & 1 == 1
-          ..[r'$even'] = index & 1 == 0;
-
-      if (row.startNode == null) {
-        var view = _boundViewFactory(childScope);
-        _rows[row.id] = row
-            ..view = view
-            ..scope = childScope
-            ..nodes = view.nodes
-            ..startNode = row.nodes[0]
-            ..endNode = row.nodes[row.nodes.length - 1];
-        _viewPort.insert(view, insertAfter: cursor);
-      }
-      cursor = row.view;
+      previousView = rows[targetIndex].view;
     }
+
+    _rows = rows;
   }
+
+  PrototypeMap _updateContext(PrototypeMap context, int index, int length) {
+    var first = (index == 0);
+    var last = (index == length - 1);
+    return context
+        ..[r'$index'] = index
+        ..[r'$first'] = first
+        ..[r'$last'] = last
+        ..[r'$middle'] = !(first || last)
+        ..[r'$odd'] = index.isOdd
+        ..[r'$even'] = index.isEven;
+  }
+}
+
+class _Row {
+  final id;
+  Scope scope;
+  View view;
+  dom.Element startNode;
+  dom.Element endNode;
+  List<dom.Element> nodes;
+
+  _Row(this.id);
 }