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

tests/corelib/growable_list_test.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.
+
+// Sanity check on the growing behavior of a growable list.
+
+import "package:expect/expect.dart";
+import "dart:collection" show IterableBase;
+
+// Iterable generating numbers in range [0..count).
+// May perform callback at some point underways.
+class TestIterableBase<E> extends IterableBase<E> {
+  final int length;
+  final int count;
+  // call [callback] if generating callbackIndex.
+  final int callbackIndex;
+  final Function callback;
+  TestIterableBase(this.length, this.count,
+                   this.callbackIndex, this.callback);
+  Iterator<E> get iterator => new CallbackIterator(this);
+}
+
+class TestIterable<E> extends TestIterableBase<E> {
+  TestIterable(count, [callbackIndex = -1, callback])
+      : super(-1, count, callbackIndex, callback);
+  int get length => throw "SHOULD NOT BE CALLED";
+}
+
+// Implement Set for private EfficientLength interface.
+@proxy  // Avoid warnings because we don't actually implement Set.
+class EfficientTestIterable<E> extends TestIterableBase<E>
+                               implements Set<E> {
+  EfficientTestIterable(length, count, [callbackIndex = -1, callback])
+      : super(length, count, callbackIndex, callback);
+}
+
+class CallbackIterator<E> implements Iterator<E> {
+  TestIterableBase _iterable;
+  int _current = null;
+  int _nextIndex = 0;
+  CallbackIterator(this._iterable);
+  bool moveNext() {
+    if (_nextIndex >= _iterable.count) {
+      _current = null;
+      return false;
+    }
+    _current = _nextIndex;
+    _nextIndex++;
+    if (_current == _iterable.callbackIndex) {
+      _iterable.callback();
+    }
+    return true;
+  }
+  int get current => _current;
+}
+
+
+void main() {
+  // Without EfficientLength interface
+  {
+    // Change length of list after 20 additions.
+    var l = [];
+    var ci = new TestIterable<E>(257, 200, () {
+      l.add("X");
+    });
+    Expect.throws(() {
+      l.addAll(ci);
+    }, (e) => e is ConcurrentModificationError);
+  }
+
+  {
+    // Change length of list after 20 additions.
+    var l = [];
+    var ci = new TestIterable<E>(257, 200, () {
+      l.length = 0;
+    });
+    Expect.throws(() {
+      l.addAll(ci);
+    }, (e) => e is ConcurrentModificationError);
+  }
+
+  // With EfficientLength interface (uses length).
+  {
+    // Change length of list after 20 additions.
+    var l = [];
+    var ci = new EfficientTestIterable<E>(257, 257, 20, () {
+      l.add("X");
+    });
+    Expect.throws(() {
+      l.addAll(ci);
+    }, (e) => e is ConcurrentModificationError);
+  }
+
+  {
+    var l = [];
+    var ci = new EfficientTestIterable<E>(257, 257, 20, () {
+      l.length = 0;
+    });
+    Expect.throws(() {
+      l.addAll(ci);
+    }, (e) => e is ConcurrentModificationError);
+  }
+
+  {
+    // Length 50, only 25 elements.
+    var l = [];
+    var ci = new EfficientTestIterable<E>(500, 250);
+    l.addAll(ci);
+    Expect.listEquals(new List.generate(250, (x)=>x), l);
+  }
+
+  {
+    // Length 25, but 50 elements.
+    var l = [];
+    var ci = new EfficientTestIterable<E>(250, 500);
+    l.addAll(ci);
+    Expect.listEquals(new List.generate(500, (x)=>x), l);
+  }
+
+  {
+    // Adding to yourself.
+    var l = [1];
+    Expect.throws(() { l.addAll(l); }, (e) => e is ConcurrentModificationError);
+  }
+
+  {
+    // Adding to yourself.
+    var l = [1, 2, 3];
+    Expect.throws(() { l.addAll(l); }, (e) => e is ConcurrentModificationError);
+  }
+}
+