// 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.Collections.Generic; using System.Threading; using System.Threading.Tasks; namespace System.Linq { public static partial class AsyncEnumerable { public static Task ContainsAsync(this IAsyncEnumerable source, TSource value, CancellationToken cancellationToken = default) => source is ICollection collection ? Task.FromResult(collection.Contains(value)) : ContainsAsync(source, value, comparer: null, cancellationToken); public static Task ContainsAsync(this IAsyncEnumerable source, TSource value, IEqualityComparer comparer, CancellationToken cancellationToken = default) { if (source == null) throw Error.ArgumentNull(nameof(source)); // // See https://github.com/dotnet/corefx/pull/25097 for the optimization here. // if (comparer == null) { return Core(source, value, cancellationToken); static async Task Core(IAsyncEnumerable _source, TSource _value, CancellationToken _cancellationToken) { #if USE_AWAIT_FOREACH await foreach (TSource item in _source.WithCancellation(_cancellationToken).ConfigureAwait(false)) { if (EqualityComparer.Default.Equals(item, _value)) { return true; } } #else var e = _source.GetAsyncEnumerator(_cancellationToken); try { while (await e.MoveNextAsync().ConfigureAwait(false)) { if (EqualityComparer.Default.Equals(e.Current, _value)) { return true; } } } finally { await e.DisposeAsync().ConfigureAwait(false); } #endif return false; } } else { return Core(source, value, comparer, cancellationToken); static async Task Core(IAsyncEnumerable _source, TSource _value, IEqualityComparer _comparer, CancellationToken _cancellationToken) { #if USE_AWAIT_FOREACH await foreach (TSource item in _source.WithCancellation(_cancellationToken).ConfigureAwait(false)) { if (_comparer.Equals(item, _value)) { return true; } } #else var e = _source.GetAsyncEnumerator(_cancellationToken); try { while (await e.MoveNextAsync().ConfigureAwait(false)) { if (_comparer.Equals(e.Current, _value)) { return true; } } } finally { await e.DisposeAsync().ConfigureAwait(false); } #endif return false; } } } } }