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quiver/lib/src/iterables/generating_iterable.dart

-// Copyright 2014 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;
-
-Iterable generate(initial(), next(o)) => new GeneratingIterable(initial, next);
-
-/**
- * An Iterable who's first value is [object] and who's subsequent values are
- * generated by passing the current value to the [next] function.
- *
- * The class is useful for creating lazy iterables from object hierarchies and
- * graphs.
- *
- * It's important that for the given initial value and next function that the
- * sequence of items eventually terminates. Otherwise calling methods that
- * expect a finite sequence, like `length` or `last`, will cause an infinite
- * loop.
- *
- * Example:
- *
- *     class Node {
- *       Node parent;
- *
- *       /**
- *        * An iterable of node and all ancestors up to the root.
- *        */
- *       Iterable<Node> ancestors =
- *           new GeneratingIterable<Node>(() => this, (n) => n.parent);
- *
- *       /**
- *        * An iterable of the root and the path of nodes to this. The reverse
- *        * of ancestors.
- *        */
- *       Iterable<Node> path = ancestors.toList().reversed();
- *     }
- *
- */
-class GeneratingIterable<T> extends IterableBase<T> {
-  final initial;
-  final next;
-
-  GeneratingIterable(T this.initial(), T this.next(T o));
-
-  @override
-  Iterator<T> get iterator => new _GeneratingIterator(initial(), next);
-}
-
-class _GeneratingIterator<T> implements Iterator<T> {
-  final next;
-  T object;
-  bool started = false;
-
-  _GeneratingIterator(T this.object, T this.next(T o));
-
-  @override
-  T get current => started ? object : null;
-
-  @override
-  bool moveNext() {
-    if (object == null) return false;
-    if (started) {
-      object = next(object);
-    } else {
-      started = true;
-    }
-    return object != null;
-  }
-}