Add collection-helpers library.

pkg/collection_helpers/lib/wrappers.dart

Index: pkg/collection_helpers/lib/wrappers.dart
diff --git a/pkg/collection_helpers/lib/wrappers.dart b/pkg/collection_helpers/lib/wrappers.dart
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+// 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.
+
+/**
+ * Delegating wrappers for [Iterable], [List], [Set], [Queue] and [Map].
+ */
+library dart.collection_helper.wrappers;
+
+import "dart:collection";
+
+/**
+ * Creates an [Iterable] that delegates all operations to a base iterable.
+ * 
+ * This class can be used hide non-`Iterable` methods of an iterable object,
+ * or it can be extended to add extra functionality on top of an existing
+ * iterable object.
+ */
+class DelegatingIterable<E> implements Iterable<E> {
+  Iterable<E> _base;
+  
+  /**
+   * Create a wrapper that forwards operations to [base].
+   */
+  DelegatingIterable(Iterable<E> base) : _base = base;

[justinfagnani, 2013/09/19 17:57:52]

FYI, we had a decent debate about constructor vs. abstract methods to get the
delegate when we added delegating collections to Quiver (A Guava-like library,
see:
https://github.com/google/quiver-dart/blob/master/lib/src/collection/delegate...)

I argued for an abstract getter named 'delegate' mainly because it allows the
subclass to swap out the delegated collection or provide it lazily, one of the
reasons you might want a wrapper, also it allows the wrapper to be used as a mix
in.

For what it's worth, this is how Guava's forwarding collections work, but there
they have protected methods.

+
+  bool any(bool test(E element)) => _base.any(test);
+
+  bool contains(Object element) => _base.contains(element);
+
+  E elementAt(int index) => _base.elementAt(index);
+
+  bool every(bool test(E element)) => _base.every(test);
+
+  Iterable expand(Iterable f(E element)) => _base.expand(f);
+
+  E get first => _base.first;
+
+  E firstWhere(bool test(E element), {E orElse()}) => 
+      _base.firstWhere(test, orElse: orElse);
+
+  fold(initialValue, combine(previousValue, E element)) =>
+      _base.fold(initialValue, combine);
+
+  void forEach(void f(E element)) => _base.forEach(f);
+
+  bool get isEmpty => _base.isEmpty;
+
+  bool get isNotEmpty => _base.isNotEmpty;
+
+  Iterator<E> get iterator => _base.iterator;
+
+  String join([String separator = ""]) => _base.join(separator);
+
+  E get last => _base.last;
+
+  E lastWhere(bool test(E element), {E orElse()}) =>
+      _base.lastWhere(test, orElse: orElse);
+
+  int get length => _base.length;
+
+  Iterable map(f(E element)) => _base.map(f);
+
+  E reduce(E combine(E value, E element)) => _base.reduce(combine);
+
+  E get single => _base.single;
+
+  E singleWhere(bool test(E element)) => _base.singleWhere(test);
+
+  Iterable<E> skip(int n) => _base.skip(n);
+
+  Iterable<E> skipWhile(bool test(E value)) => _base.skipWhile(test);
+
+  Iterable<E> take(int n) => _base.take(n);
+
+  Iterable<E> takeWhile(bool test(E value)) => _base.takeWhile(test);
+
+  List<E> toList({bool growable: true}) => _base.toList(growable: growable);
+
+  Set<E> toSet() => _base.toSet();
+
+  Iterable<E> where(bool test(E element)) => _base.where(test);
+}
+
+
+/**
+ * Creates a [List] that delegates all operations to a base list.
+ * 
+ * This class can be used hide non-`List` methods of a list object,
+ * or it can be extended to add extra functionality on top of an existing
+ * list object.
+ */
+class DelegatingList<E> extends DelegatingIterable<E> implements List<E> {
+  DelegatingList(List<E> base) : super(base);
+  
+  List<E> get _listBase => _base;
+  
+  E operator [](int index) => _listBase[index];
+
+  void operator []=(int index, E value) {
+    _listBase[index] = value;
+  }
+
+  void add(E value) {
+    _listBase.add(value);
+  }
+
+  void addAll(Iterable<E> iterable) {
+    _listBase.addAll(iterable);
+  }
+
+  Map<int, E> asMap() => _listBase.asMap();
+
+  void clear() {
+    _listBase.clear();
+  }
+
+  void fillRange(int start, int end, [E fillValue]) {
+    _listBase.fillRange(start, end, fillValue);
+  }
+
+  Iterable<E> getRange(int start, int end) => _listBase.getRange(start, end);
+
+  int indexOf(E element, [int start = 0]) => _listBase.indexOf(element, start);
+
+  void insert(int index, E element) {
+    _listBase.insert(index, element);
+  }
+
+  void insertAll(int index, Iterable<E> iterable) {
+    _listBase.insertAll(index, iterable);
+  }
+
+  int lastIndexOf(E element, [int start]) => 
+      _listBase.lastIndexOf(element, start);
+
+  void set length(int newLength) {
+    _listBase.length = newLength;
+  }
+
+  bool remove(Object value) => _listBase.remove(value);
+
+  E removeAt(int index) => _listBase.removeAt(index);
+
+  E removeLast() => _listBase.removeLast();
+
+  void removeRange(int start, int end) {
+    _listBase.removeRange(start, end);
+  }
+
+  void removeWhere(bool test(E element)) {
+    _listBase.removeWhere(test);
+  }
+
+  void replaceRange(int start, int end, Iterable<E> iterable) {
+    _listBase.replaceRange(start, end, iterable);
+  }
+
+  void retainWhere(bool test(E element)) {
+    _listBase.retainWhere(test);
+  }
+
+  Iterable<E> get reversed => _listBase.reversed;
+
+  void setAll(int index, Iterable<E> iterable) {
+    _listBase.setAll(index, iterable);
+  }
+
+  void setRange(int start, int end, Iterable<E> iterable, [int skipCount = 0]) {
+    _listBase.setRange(start, end, iterable, skipCount);
+  }
+
+  void sort([int compare(E a, E b)]) {
+    _listBase.sort(compare);
+  }
+
+  List<E> sublist(int start, [int end]) => _listBase.sublist(start, end);
+}
+
+
+/**
+ * Creates a [Set] that delegates all operations to a base set.
+ * 
+ * This class can be used hide non-`Set` methods of a set object,
+ * or it can be extended to add extra functionality on top of an existing
+ * set object.
+ */
+class DelegatingSet<E> extends DelegatingIterable<E> implements Set<E> {
+  DelegatingSet(Set<E> base) : super(base);
+  
+  Set<E> get _setBase => _base;
+
+  void add(E value) {
+    _setBase.add(value);
+  }
+
+  void addAll(Iterable<E> elements) {
+    _setBase.addAll(elements);
+  }
+
+  void clear() {
+    _setBase.clear();
+  }
+
+  bool containsAll(Iterable<Object> other) => _setBase.containsAll(other);
+
+  Set<E> difference(Set<E> other) => _setBase.difference(other);
+
+  Set<E> intersection(Set<Object> other) => _setBase.intersection(other);
+
+  bool remove(Object value) => _setBase.remove(value);
+
+  void removeAll(Iterable<Object> elements) {
+    _setBase.removeAll(elements);
+  }
+
+  void removeWhere(bool test(E element)) {
+    _setBase.removeWhere(test);
+  }
+
+  void retainAll(Iterable<Object> elements) {
+    _setBase.retainAll(elements);
+  }
+
+  void retainWhere(bool test(E element)) {
+    _setBase.retainWhere(test);
+  }
+
+  Set<E> union(Set<E> other) => _setBase.union(other);
+}
+
+/**
+ * Creates a [Queue] that delegates all operations to a base queue.
+ * 
+ * This class can be used hide non-`Queue` methods of a queue object,
+ * or it can be extended to add extra functionality on top of an existing
+ * queue object.
+ */
+class DelegatingQueue<E> extends DelegatingIterable<E> implements Queue<E> {
+  DelegatingQueue(Queue<E> queue) : super(queue);
+ 
+  Queue get _baseQueue => _base;
+  
+  void add(E value) {
+    _baseQueue.add(value);
+  }
+
+  void addAll(Iterable<E> iterable) {
+    _baseQueue.addAll(iterable);
+  }
+
+  void addFirst(E value) {
+    _baseQueue.addFirst(value); 
+  }
+
+  void addLast(E value) {
+    _baseQueue.addLast(value);
+  }
+
+  void clear() {
+    _baseQueue.clear();
+  }
+
+  bool remove(Object object) => _baseQueue.remove(object);
+
+  E removeFirst() => _baseQueue.removeFirst();
+
+  E removeLast() => _baseQueue.removeLast();
+}
+
+/**
+ * Creates a [Map] that delegates all operations to a base map.
+ * 
+ * This class can be used hide non-`Map` methods of an object that extends 
+ * `Map`, or it can be extended to add extra functionality on top of an existing
+ * map object.
+ */
+class DelegatingMap<K, V> implements Map<K, V> {
+  Map<K, V> _base;
+  DelegatingMap(Map<K, V> base) : _base = base;
+  
+  V operator [](Object key) => _base[key];
+
+  void operator []=(K key, V value) {
+    _base[key] = value;
+  }
+
+  void addAll(Map<K, V> other) {
+    _base.addAll(other);
+  }
+
+  void clear() {
+    _base.clear();
+  }
+
+  bool containsKey(Object key) => _base.containsKey(key);
+
+  bool containsValue(Object value) => _base.containsValue(value);
+
+  void forEach(void f(K key, V value)) {
+    _base.forEach(f);
+  }
+
+  bool get isEmpty => _base.isEmpty;
+
+  bool get isNotEmpty => _base.isNotEmpty;
+
+  Iterable<K> get keys => _base.keys;
+
+  int get length => _base.length;
+
+  V putIfAbsent(K key, V ifAbsent()) => _base.putIfAbsent(key, ifAbsent);
+
+  V remove(Object key) => _base.remove(key);
+
+  Iterable<V> get values => _base.values;
+}