Warnings for instantiating an abstract type.

frog/utils.dart

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // Collection<T> supports most of the ES 5 Array methods, but it's missing
 // map and reduce.
 
 // TODO(jmesserly): we might want a version of this that return an iterable,
 // however JS, Python and Ruby versions are all eager.
-List map(Iterable source, mapper(source)) {
-  List result = new List();
+List map(Iterable source, Dynamic mapper(source)) {
+  List result = [];
   if (source is List) {
     List list = source; // TODO: shouldn't need this
     result.length = list.length;
     for (int i = 0; i < list.length; i++) {
       result[i] = mapper(list[i]);
     }
   } else {
     for (final item in source) {
       result.add(mapper(item));
     }
   }
   return result;
 }
 
 reduce(Iterable source, callback, [initialValue]) {
   final i = source.iterator();
 
   var current = initialValue;
   if (current == null && i.hasNext()) {
     current = i.next();
   }
   while (i.hasNext()) {
     current = callback(current, i.next());
   }
   return current;
 }
 
-List zip(Iterable left, Iterable right, mapper(left, right)) {
-  List result = new List();
+List zip(Iterable left, Iterable right, Dynamic mapper(left, right)) {
+  List result = [];
   var x = left.iterator();
   var y = right.iterator();
   while (x.hasNext() && y.hasNext()) {
     result.add(mapper(x.next(), y.next()));
   }
   if (x.hasNext() || y.hasNext()) {
     throw new IllegalArgumentException();
   }
   return result;
 }
 
+Map<Dynamic, List> groupBy(Iterable left, Dynamic keyFn(value)) {
+  Map result = {};
+  var iter = left.iterator();
+  while (iter.hasNext()) {
+    var i = iter.next();
+    result.putIfAbsent(keyFn(i), () => []).add(i);
+  }
+  return result;
+}
+
 /** Sorts the map by the key. */
 List orderValuesByKeys(Map map) {
   // TODO(jmesserly): it'd be nice to have SortedMap in corelib.
   List keys = map.getKeys();
   keys.sort((x, y) => x.compareTo(y));
   final values = [];
   for (var k in keys) {
     values.add(map[k]);
   }
   return values;
@@ skipping 64 matching lines @@
   final int length;
   int _index = 0;
   FixedIterator(this.value, this.length);
 
   bool hasNext() => _index < length;
   E next() {
     _index++;
     return value;
   }
 }