1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253545556575859606162636465666768 |
- // // Licensed to the .NET Foundation under one or more agreements.
- // // The .NET Foundation licenses this file to you under the Apache 2.0 License.
- // // See the LICENSE file in the project root for more information.
- using System;
- using System.Collections.Generic;
- using System.Linq;
- using System.Threading;
- using System.Threading.Tasks;
- namespace System.Linq
- {
- public static partial class AsyncEnumerable
- {
- public static IAsyncEnumerable<TSource> DefaultIfEmpty<TSource>(this IAsyncEnumerable<TSource> source, TSource defaultValue)
- {
- if (source == null)
- throw new ArgumentNullException(nameof(source));
- return Create(() =>
- {
- var done = false;
- var hasElements = false;
- var e = source.GetEnumerator();
- var current = default(TSource);
- var cts = new CancellationTokenDisposable();
- var d = Disposable.Create(cts, e);
- var f = default(Func<CancellationToken, Task<bool>>);
- f = async ct =>
- {
- if (done)
- return false;
- if (await e.MoveNext(ct)
- .ConfigureAwait(false))
- {
- hasElements = true;
- current = e.Current;
- return true;
- }
- done = true;
- if (!hasElements)
- {
- current = defaultValue;
- return true;
- }
- return false;
- };
- return Create(
- f,
- () => current,
- d.Dispose,
- e
- );
- });
- }
- public static IAsyncEnumerable<TSource> DefaultIfEmpty<TSource>(this IAsyncEnumerable<TSource> source)
- {
- if (source == null)
- throw new ArgumentNullException(nameof(source));
- return source.DefaultIfEmpty(default(TSource));
- }
- }
- }
|