Support for observable models, fixes #259

lib/observe/list.dart

+// Copyright (c) 2013, 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.
+
+library web_ui.observe.list;
+
+import 'dart:collection';
+import 'package:web_ui/observe.dart';
+
+// TODO(jmesserly): this should extend the real list implementation.
+// See http://dartbug.com/2600. The workaround was to copy+paste lots of code
+// from the VM.
+/**
+ * Represents an observable list of model values. If any items are added,
+ * removed, or replaced, then observers that are registered with
+ * [observe] will be notified.
+ */
+class ObservableList<E> extends Collection<E> implements List<E> {
+  /** The inner [List<E>] with the actual storage. */
+  final List<E> _list;
+
+  final List<Object> _observeIndex;
+  Object _observeLength;
+
+  /**
+   * Creates an observable list of the given [length].
+   *
+   * If no [length] argument is supplied an extendable list of
+   * length 0 is created.
+   *
+   * If a [length] argument is supplied, a fixed size list of that
+   * length is created.
+   */
+  ObservableList([int length = 0])
+      : _list = new List<E>(length),
+        _observeIndex = new List<Object>(length);
+
+  /**
+   * Creates an observable list with the elements of [other]. The order in
+   * the list will be the order provided by the iterator of [other].
+   */
+  factory ObservableList.from(Iterable<E> other) =>
+      new ObservableList<E>()..addAll(other);
+
+  // TODO(jmesserly): This should be on List.
+  // See http://code.google.com/p/dart/issues/detail?id=947

[Siggi Cherem (dart-lang), 2013/02/13 01:43:24]

947 seems to be marked as fixed... it seems that 'void remove(Object)' is in
Collection.

[Jennifer Messerly, 2013/02/13 05:43:15]

yeah. It seems to be abstract though, so we still need an implementation.
Removed the TODO though.

+  bool remove(E item) {
+    int i = indexOf(item);
+    if (i == -1) return false;
+    removeAt(i);
+    return true;
+  }
+
+  // TODO(jmesserly): This should be on List, to match removeAt.
+  // See http://code.google.com/p/dart/issues/detail?id=5375
+  void insertAt(int index, E item) => insertRange(index, 1, item);
+
+  bool contains(E item) => Collections.contains(_list, item);

[Siggi Cherem (dart-lang), 2013/02/13 01:43:24]

Are you using Collections to skip over any overhead from observables that comes
from using _list.contains(item)?

[Jennifer Messerly, 2013/02/13 05:43:15]

I think _list.contains would have less overhead. But Collections.contains will
use our []-indexer, and cause read notifications to happen.

It'll make more sense when I move it down (as you suggested)

+
+  E get first => this[0];
+
+  Iterator<E> get iterator => new ListIterator<E>(this);
+
+  int get length {
+    if (observeReads) _observeLength = notifyRead(_observeLength);
+    return _list.length;
+  }
+
+  set length(int value) {
+    if (length == value) return;
+
+    if (_observeLength != null) _observeLength = notifyWrite(_observeLength);
+
+    // If we are shrinking the list, explicitly null out items so we track
+    // the change to those items.
+    for (int i = value; i < _list.length; i++) {
+      this[i] = null;
+    }
+    _observeIndex.length = value;
+    _list.length = value;
+  }
+
+  E operator [](int index) {
+    if (observeReads) _observeIndex[index] = notifyRead(_observeIndex[index]);
+    return _list[index];
+  }
+
+  operator []=(int index, E value) {
+    var observer = _observeIndex[index];
+    var oldValue = _list[index];
+    if (observer != null && oldValue != value) {
+      _observeIndex[index] = notifyWrite(observer);
+    }
+    _list[index] = value;
+  }
+
+  void add(E value) {
+    if (_observeLength != null) _observeLength = notifyWrite(_observeLength);
+    _list.add(value);
+    _observeIndex.add(null);
+  }
+
+  // ---------------------------------------------------------------------------
+  // Note: below this comment, methods are either:
+  //   * redirect to Arrays
+  //   * redirect to Collections
+  //   * copy+paste from VM GrowableObjectArray.
+  // The general idea is to have these methods operate in terms of our primitive
+  // methods above, so they correctly track reads/writes.

[Siggi Cherem (dart-lang), 2013/02/13 01:43:24]

consider moving contains, insertAt, first, and iterator below this line?

[Jennifer Messerly, 2013/02/13 05:43:15]

good call

+  // ---------------------------------------------------------------------------
+
+  E removeLast() {
+    var len = length - 1;
+    var elem = this[len];
+    length = len;
+    return elem;
+  }
+
+  int indexOf(E element, [int start = 0]) =>
+      Arrays.indexOf(this, element, start, length);
+
+  int lastIndexOf(E element, [int start]) =>
+      Arrays.lastIndexOf(this, element, start);
+
+  ObservableList<E> getRange(int start, int length)  {
+    if (length == 0) return [];
+    Arrays.rangeCheck(this, start, length);
+    List list = new ObservableList<E>(length);
+    Arrays.copy(this, start, list, 0, length);
+    return list;
+  }
+
+  bool get isEmpty => length == 0;
+
+  E get last => this[length - 1];
+
+  void addLast(E value) => add(value);
+
+  void addAll(Iterable<E> collection) {
+    for (E elem in collection) {
+      add(elem);
+    }
+  }
+
+  void sort([compare = Comparable.compare]) =>
+      IterableMixinWorkaround.sortList(this, compare);
+
+  List<E> get reversed => IterableMixinWorkaround.reversedList(this);
+
+  void clear() {
+    this.length = 0;
+  }
+
+  E removeAt(int index) {
+    if (index is! int) throw new ArgumentError(index);
+    E result = this[index];
+    int newLength = this.length - 1;
+    Arrays.copy(this,
+                index + 1,
+                this,
+                index,
+                newLength - index);
+    this.length = newLength;
+    return result;
+  }
+
+  void setRange(int start, int length, List<E> from, [int startFrom = 0]) {
+    Arrays.copy(from, startFrom, this, start, length);
+  }
+
+  void removeRange(int start, int length) {
+    if (length == 0) {
+      return;
+    }
+    Arrays.rangeCheck(this, start, length);
+    Arrays.copy(this,
+                start + length,
+                this,
+                start,
+                this.length - length - start);
+    this.length = this.length - length;
+  }
+
+  void insertRange(int start, int length, [E initialValue]) {
+    if (length == 0) {
+      return;
+    }
+    if ((length < 0) || (length is! int)) {
+      throw new ArgumentError("invalid length specified $length");
+    }
+    if (start < 0 || start > this.length) {
+      throw new RangeError.value(start);
+    }
+    var oldLength = this.length;
+    this.length = oldLength + length;  // Will expand if needed.
+    Arrays.copy(this,
+                start,
+                this,
+                start + length,
+                oldLength - start);
+    for (int i = start; i < start + length; i++) {
+      this[i] = initialValue;
+    }
+  }
+
+  String toString() => Collections.collectionToString(this);
+}
+
+// TODO(jmesserly): copy+paste from collection-dev

[Siggi Cherem (dart-lang), 2013/02/13 01:43:24]

I assume collection-dev can't be used, or we shoudln't use it?

[Jennifer Messerly, 2013/02/13 05:43:15]

yup. According to Florian/Lasse everything you need for implementing
List/Iterable etc, will be exposed through dart:collections. it's a work in
progress at the moment.

+/**
+ * Iterates over a [List] in growing index order.
+ */
+class ListIterator<E> implements Iterator<E> {
+  final List<E> _list;
+  final int _length;
+  int _position;
+  E _current;
+
+  ListIterator(List<E> list)
+      : _list = list, _position = -1, _length = list.length;
+
+  bool moveNext() {
+    if (_list.length != _length) {
+      throw new ConcurrentModificationError(_list);
+    }
+    int nextPosition = _position + 1;
+    if (nextPosition < _length) {
+      _position = nextPosition;
+      _current = _list[nextPosition];
+      return true;
+    }
+    _current = null;
+    return false;
+  }
+
+  E get current => _current;
+}