Merge branch 'simon-void.master'
Closes #20
Closes #31
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 559e810..de42222 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+## 1.7.0
+
+* Add a `const UnmodifiableSetView.empty()` constructor.
+
## 1.6.0
* Add a `UnionSet` class that provides a view of the union of a set of sets.
diff --git a/lib/src/empty_unmodifiable_set.dart b/lib/src/empty_unmodifiable_set.dart
new file mode 100644
index 0000000..581532f
--- /dev/null
+++ b/lib/src/empty_unmodifiable_set.dart
@@ -0,0 +1,40 @@
+// Copyright (c) 2016, 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.
+
+import 'dart:collection';
+
+import 'unmodifiable_wrappers.dart';
+
+// Unfortunately, we can't use UnmodifiableSetMixin here, since const classes
+// can't use mixins.
+/// An unmodifiable, empty set that can have a const constructor.
+class EmptyUnmodifiableSet<E> extends IterableBase<E>
+ implements UnmodifiableSetView<E> {
+ static /*=T*/ _throw/*<T>*/() {
+ throw new UnsupportedError("Cannot modify an unmodifiable Set");
+ }
+
+ Iterator<E> get iterator => new Iterable<E>.empty().iterator;
+ int get length => 0;
+
+ const EmptyUnmodifiableSet();
+
+ bool contains(Object element) => false;
+ bool containsAll(Iterable<Object> other) => other.isEmpty;
+ E lookup(Object element) => null;
+ Set<E> toSet() => new Set();
+ Set<E> union(Set<E> other) => new Set.from(other);
+ Set<E> intersection(Set<Object> other) => new Set();
+ Set<E> difference(Set<Object> other) => new Set();
+
+ bool add(E value) => _throw();
+ void addAll(Iterable<E> elements) => _throw();
+ void clear() => _throw();
+ bool remove(Object element) => _throw();
+ void removeAll(Iterable<Object> elements) => _throw();
+ void removeWhere(bool test(E element)) => _throw();
+ void retainWhere(bool test(E element)) => _throw();
+ void retainAll(Iterable<Object> elements) => _throw();
+}
+
diff --git a/lib/src/unmodifiable_wrappers.dart b/lib/src/unmodifiable_wrappers.dart
index 6003286..5efbee4 100644
--- a/lib/src/unmodifiable_wrappers.dart
+++ b/lib/src/unmodifiable_wrappers.dart
@@ -5,6 +5,7 @@
export "dart:collection" show UnmodifiableListView, UnmodifiableMapView;
import 'wrappers.dart';
+import 'empty_unmodifiable_set.dart';
/// A fixed-length list.
///
@@ -91,8 +92,14 @@
/// such as [add] and [remove], throw an [UnsupportedError].
/// Permitted operations defer to the wrapped set.
class UnmodifiableSetView<E> extends DelegatingSet<E>
- with UnmodifiableSetMixin<E> {
+ with UnmodifiableSetMixin<E> {
UnmodifiableSetView(Set<E> setBase) : super(setBase);
+
+ /// An unmodifiable empty set.
+ ///
+ /// This is the same as `new UnmodifiableSetView(new Set())`, except that it
+ /// can be used in const contexts.
+ const factory UnmodifiableSetView.empty() = EmptyUnmodifiableSet<E>;
}
/// Mixin class that implements a throwing version of all set operations that
diff --git a/pubspec.yaml b/pubspec.yaml
index 992e7ae..7c88550 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,5 +1,5 @@
name: collection
-version: 1.6.0
+version: 1.7.0
author: Dart Team <misc@dartlang.org>
description: Collections and utilities functions and classes related to collections.
homepage: https://www.github.com/dart-lang/collection
diff --git a/test/unmodifiable_collection_test.dart b/test/unmodifiable_collection_test.dart
index 682a406..cdb5101 100644
--- a/test/unmodifiable_collection_test.dart
+++ b/test/unmodifiable_collection_test.dart
@@ -35,6 +35,8 @@
Set aSet = new Set();
testUnmodifiableSet(aSet, new UnmodifiableSetView(aSet), "empty");
+ aSet = new Set();
+ testUnmodifiableSet(aSet, const UnmodifiableSetView.empty(), "const empty");
aSet = new Set.from([42]);
testUnmodifiableSet(aSet, new UnmodifiableSetView(aSet), "single-42");
aSet = new Set.from([7]);
