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quiver/lib/src/iterables/enumerate.dart

-// Copyright 2013 Google Inc. All Rights Reserved.
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//     http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-part of quiver.iterables;
-
-/**
- * Returns an [Iterable] of [IndexedValue]s where the nth value holds the nth
- * element of [iterable] and its index.
- */
-Iterable<IndexedValue> enumerate(Iterable iterable) =>
-    new EnumerateIterable(iterable);
-
-class IndexedValue<V> {
-  final int index;
-  final V value;
-
-  IndexedValue(this.index, this.value);
-
-  operator ==(o) => o is IndexedValue && o.index == index && o.value == value;
-  int get hashCode => index * 31 + value.hashCode;
-  String toString() => '($index, $value)';
-}
-
-/**
- * An [Iterable] of [IndexedValue]s where the nth value holds the nth
- * element of [iterable] and its index. See [enumerate].
- */
-// This was inspired by MappedIterable internal to Dart collections.
-class EnumerateIterable<V> extends IterableBase<IndexedValue<V>> {
-  final Iterable<V> _iterable;
-
-  EnumerateIterable(this._iterable);
-
-  Iterator<IndexedValue<V>> get iterator =>
-      new EnumerateIterator<V>(_iterable.iterator);
-
-  // Length related functions are independent of the mapping.
-  int get length => _iterable.length;
-  bool get isEmpty => _iterable.isEmpty;
-
-  // Index based lookup can be done before transforming.
-  IndexedValue<V> get first => new IndexedValue<V>(0, _iterable.first);
-  IndexedValue<V> get last => new IndexedValue<V>(length - 1, _iterable.last);
-  IndexedValue<V> get single => new IndexedValue<V>(0, _iterable.single);
-  IndexedValue<V> elementAt(int index) =>
-      new IndexedValue<V>(index, _iterable.elementAt(index));
-}
-
-/** The [Iterator] returned by [EnumerateIterable.iterator]. */
-class EnumerateIterator<V> extends Iterator<IndexedValue<V>> {
-  final Iterator<V> _iterator;
-  int _index = 0;
-  IndexedValue<V> _current;
-
-  EnumerateIterator(this._iterator);
-
-  IndexedValue<V> get current => _current;
-
-  bool moveNext() {
-    if (_iterator.moveNext()) {
-      _current = new IndexedValue(_index++, _iterator.current);
-      return true;
-    }
-    _current = null;
-    return false;
-  }
-}