| // 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 collections; |
| |
| /** |
| * Returns the concatentation of the input iterables. |
| * |
| * The returned iterable is a lazily-evaluated view on the input iterables. |
| */ |
| Iterable concat(Iterable<Iterable> iterables) => iterables.expand((x) => x); |
| |
| |
| /** |
| * Returns the concatentation of the input iterables as a [List]. |
| */ |
| List concatToList(Iterable<Iterable> iterables) => concat(iterables).toList(); |
| |
| |
| /** |
| * Returns the given [list] if it is not empty, or `null` otherwise. |
| */ |
| List nullIfEmpty(List list) { |
| if (list == null) { |
| return null; |
| } |
| if (list.isEmpty) { |
| return null; |
| } |
| return list; |
| } |