Optimize List.toList/.sublist and List.from on lists.

runtime/lib/array.dart

 // Copyright (c) 2012, 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.
 
 
 // TODO(srdjan): Use shared array implementation.
 class _List<E> implements List<E> {
 
   factory _List(length) native "List_allocate";
 
@@ skipping 49 matching lines @@
   void setRange(int start, int end, Iterable<E> iterable, [int skipCount = 0]) {
     if (start < 0 || start > this.length) {
       throw new RangeError.range(start, 0, this.length);
     }
     if (end < start || end > this.length) {
       throw new RangeError.range(end, start, this.length);
     }
     int length = end - start;
     if (length == 0) return;
 
     if (ClassID.getID(iterable) == ClassID.cidOneByteString) {

[Lasse Reichstein Nielsen, 2014/08/19 12:48:30]

This looks wrong: OneByteString?

       _copyFromObjectArray(iterable, skipCount, start, length);
     } else {
       if (iterable is List) {
         Lists.copy(iterable, skipCount, this, start, length);
       } else {
         Iterator it = iterable.iterator;
         while (skipCount > 0) {
           if (!it.moveNext()) return;
           skipCount--;
         }
@@ skipping 14 matching lines @@
   }
 
   void fillRange(int start, int end, [E fillValue]) {
     IterableMixinWorkaround.fillRangeList(this, start, end, fillValue);
   }
 
   List<E> sublist(int start, [int end]) {
     Lists.indicesCheck(this, start, end);
     if (end == null) end = this.length;
     int length = end - start;
-    if (start == end) return [];
-    List list = new _GrowableList<E>.withCapacity(length);
-    list.length = length;
-    Lists.copy(this, start, list, 0, length);
-    return list;
+    if (start == end) return <E>[];
+    List list = new _List(length);
+    list._copyFromObjectArray(this, start, 0, length);
+    var result = new _GrowableList<E>.withData(list);
+    result._setLength(length);
+    return result;
   }
 
   // Iterable interface.
 
   bool contains(Object element) {
     return IterableMixinWorkaround.contains(this, element);
   }
 
   void forEach(f(E element)) {
     IterableMixinWorkaround.forEach(this, f);
@@ skipping 122 matching lines @@
     if (length > 0) return this[length - 1];
     throw IterableElementError.noElement();
   }
 
   E get single {
     if (length == 1) return this[0];
     if (length == 0) throw IterableElementError.noElement();
     throw IterableElementError.tooMany();
   }
 
-  List<E> toList({ bool growable: true}) {
-    return new List<E>.from(this, growable: growable);
+  List<E> toList({ bool growable: true }) {
+    var length = this.length;
+    var result = growable ? new _List(length) : new _List<E>(length);
+    result._copyFromObjectArray(this, 0, 0, length);
+    if (growable) {
+      result = new _GrowableList<E>.withData(result);
+      result._setLength(length);
+    }
+    return result;
   }
 
   Set<E> toSet() {
     return new Set<E>.from(this);
   }
 
   Map<int, E> asMap() {
     return new IterableMixinWorkaround<E>().asMapList(this);
   }
 }
@@ skipping 69 matching lines @@
   }
 
   void replaceRange(int start, int end, Iterable<E> iterable) {
     throw UnmodifiableListError.change();
   }
 
   List<E> sublist(int start, [int end]) {
     Lists.indicesCheck(this, start, end);
     if (end == null) end = this.length;
     int length = end - start;
-    if (start == end) return [];
-    List list = new List<E>();
-    list.length = length;
+    if (start == end) return <E>[];
+    List list = new _List(length);
     Lists.copy(this, start, list, 0, length);
-    return list;
+    var result = new _GrowableList<E>.withData(list);
+    result._setLength(length);
+    return result;
   }
 
   Iterable<E> getRange(int start, int end) {
     return new IterableMixinWorkaround<E>().getRangeList(this, start, end);
   }
 
   // Collection interface.
 
   bool contains(Object element) {
     return IterableMixinWorkaround.contains(this, element);
@@ skipping 131 matching lines @@
     throw IterableElementError.noElement();
   }
 
   E get single {
     if (length == 1) return this[0];
     if (length == 0) throw IterableElementError.noElement();
     throw IterableElementError.tooMany();
   }
 
   List<E> toList({ bool growable: true }) {
-    return new List<E>.from(this, growable: growable);
+    int length = this.length;
+    List list = growable ? new _GrowableList<E>(length) : new _List<E>(length);
+    Lists.copy(this, 0, list, 0, length);
+    return list;
   }
 
   Set<E> toSet() {
     return new Set<E>.from(this);
   }
 
   Map<int, E> asMap() {
     return new IterableMixinWorkaround<E>().asMapList(this);
   }
 }
@@ skipping 20 matching lines @@
     }
     _position = _length;
     _current = null;
     return false;
   }
 
   E get current {
     return _current;
   }
 }