| // 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 concatenation of the input [iterables]. |
| * |
| * The returned iterable is a lazily-evaluated view on the input iterables. |
| */ |
| Iterable/*<E>*/ concat/*<E>*/(Iterable<Iterable/*<E>*/ > iterables) => |
| iterables.expand((x) => x); |
| |
| /** |
| * Returns the concatenation of the input [iterables] as a [List]. |
| */ |
| List/*<E>*/ concatToList/*<E>*/(Iterable<Iterable/*<E>*/ > iterables) => |
| concat(iterables).toList(); |
| |
| /** |
| * Returns the given [list] if it is not empty, or `null` otherwise. |
| */ |
| List/*<E>*/ nullIfEmpty/*<E>*/(List/*<E>*/ list) { |
| if (list == null) { |
| return null; |
| } |
| if (list.isEmpty) { |
| return null; |
| } |
| return list; |
| } |
| |
| /// A pair of values. |
| class Pair<E, F> { |
| final E first; |
| final F last; |
| |
| Pair(this.first, this.last); |
| |
| int get hashCode => first.hashCode ^ last.hashCode; |
| |
| bool operator ==(other) { |
| if (other is! Pair) return false; |
| return other.first == first && other.last == last; |
| } |
| |
| String toString() => '($first, $last)'; |
| } |