Add new constructors to YamlNode subclasses.

pkg/yaml/lib/src/yaml_node_wrapper.dart

+// Copyright (c) 2014, 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 yaml.yaml_node_wrapper;
+
+import 'dart:collection';
+
+import 'package:collection/collection.dart' as pc;

[Bob Nystrom, 2014/06/21 00:14:15]

Why "pc"? How about "collection"?

[nweiz, 2014/06/23 22:23:07]

"pc" is for "package collection". Just calling it "collection" is confusing
because the point of prefixing it in the first place is to disambiguate between
two collection libraries.

[Bob Nystrom, 2014/06/23 23:11:44]

I didn't infer that abbreviation at all. The other import isn't prefixed, so
it's not like "collection" is in use. If you don't want that, at least,
"pkg_collection" or something along those lines. "pc" didn't mean anything to
me.

[nweiz, 2014/06/24 00:03:09]

The point of using a prefix is to make it clear where the name is coming from,
and "collection" doesn't do that when there are two collections libraries.
That's so verbose, but done.

+import 'package:source_maps/source_maps.dart';
+
+import 'dummy_span.dart';
+import 'yaml_node.dart';
+
+/// A wrapper that makes a normal Dart map behave like a [YamlMap].
+class YamlMapWrapper extends MapBase
+    with pc.UnmodifiableMapMixin<dynamic, YamlNode>
+    implements YamlMap {
+  final Map _dartMap;
+
+  final Span span;
+
+  final Map<dynamic, YamlNode> nodes;
+
+  Map get value => this;
+
+  Iterable get keys => _dartMap.keys;
+
+  YamlMapWrapper(Map dartMap, String sourceName)
+      : this._(dartMap, new DummySpan(sourceName));
+
+  YamlMapWrapper._(Map dartMap, Span span)
+      : _dartMap = dartMap,
+        span = span,
+        nodes = new _YamlMapNodes(dartMap, span);
+
+  operator [](Object key) {
+    var value = _dartMap[key];
+    if (value is Map) return new YamlMapWrapper._(value, span);
+    if (value is List) return new YamlListWrapper._(value, span);

[Bob Nystrom, 2014/06/21 00:14:15]

Since the wrapper classes don't implement equality, returning a new one each
time can cause some surprising behavior:

var map = new YamlMap.wrap({"key": {"inner": "map"});
print(map["key"] == map["key"]); // false

We could memoize the wrapped objects, or maybe implement equality. The former
has better semantics but worse memory usage. What do you think?

[nweiz, 2014/06/23 22:23:07]

I like implementing equality in terms of the wrapped objects' equality. Done.

+    return value;
+  }
+}
+
+/// The implementation of [YamlMapWrapper.nodes] as a wrapper around the Dart
+/// map.
+class _YamlMapNodes extends MapBase<dynamic, YamlNode>
+    with pc.UnmodifiableMapMixin<dynamic, YamlNode> {
+  final Map _dartMap;
+
+  final Span _span;
+
+  Iterable get keys =>
+      _dartMap.keys.map((key) => new YamlScalar.internal(key, _span));
+
+  _YamlMapNodes(this._dartMap, this._span);
+
+  YamlNode operator [](Object key) {
+    if (key is YamlScalar) key = key.value;
+    if (!_dartMap.containsKey(key)) return null;
+    var value = _dartMap[key];
+    if (value is Map) return new YamlMapWrapper._(value, _span);
+    if (value is List) return new YamlListWrapper._(value, _span);

[Bob Nystrom, 2014/06/21 00:14:15]

Encapsulate this little blob of logic in a helper fn and use here and below.

[nweiz, 2014/06/23 22:23:07]

Done.

+    return new YamlScalar.internal(value, _span);
+  }
+}
+
+// TODO(nweiz): Use UnmodifiableListMixin when issue 18970 is fixed.
+/// A wrapper that makes a normal Dart list behave like a [YamlList].
+class YamlListWrapper extends ListBase implements YamlList {
+  final List _dartList;
+
+  final Span span;
+
+  final List<YamlNode> nodes;
+
+  List get value => this;
+
+  int get length => _dartList.length;
+
+  set length(int index) {
+    throw new UnsupportedError("Cannot modify an unmodifiable List");

[Bob Nystrom, 2014/06/21 00:14:15]

"."

[nweiz, 2014/06/23 22:23:07]

Done, although this now doesn't match the "dart:" unmodifiable views' error
messages.

[Bob Nystrom, 2014/06/23 23:11:44]

Ugh. Well, these are better. :)

+  }
+
+  YamlListWrapper(List dartList, String sourceName)
+      : this._(dartList, new DummySpan(sourceName));
+
+  YamlListWrapper._(List dartList, Span span)
+      : _dartList = dartList,
+        span = span,
+        nodes = new _YamlListNodes(dartList, span);
+
+  operator [](int index) {
+    var value = _dartList[index];
+    if (value is Map) return new YamlMapWrapper._(value, span);
+    if (value is List) return new YamlListWrapper._(value, span);
+    return value;
+  }
+
+  operator []=(int index, value) {
+    throw new UnsupportedError("Cannot modify an unmodifiable List");

[Bob Nystrom, 2014/06/21 00:14:15]

"."

[nweiz, 2014/06/23 22:23:07]

Done.

+  }
+}
+
+// TODO(nweiz): Use UnmodifiableListMixin when issue 18970 is fixed.
+/// The implementation of [YamlListWrapper.nodes] as a wrapper around the Dart
+/// list.
+class _YamlListNodes extends ListBase<YamlNode> {
+  final List _dartList;
+
+  final Span _span;
+
+  int get length => _dartList.length;
+
+  set length(int index) {
+    throw new UnsupportedError("Cannot modify an unmodifiable List");
+  }
+
+  _YamlListNodes(this._dartList, this._span);
+
+  YamlNode operator [](int index) {
+    var value = _dartList[index];
+    if (value is Map) return new YamlMapWrapper._(value, _span);
+    if (value is List) return new YamlListWrapper._(value, _span);
+    return new YamlScalar.internal(value, _span);
+  }
+
+  operator []=(int index, value) {
+    throw new UnsupportedError("Cannot modify an unmodifiable List");
+  }
+}