reactive/Ix.NET/Source/System.Linq.Async/System/Linq/Operators/ToHashSet.cs

// 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<HashSet<TSource>> ToHashSetAsync<TSource>(this IAsyncEnumerable<TSource> source, CancellationToken cancellationToken = default)
        {
            if (source == null)
                throw Error.ArgumentNull(nameof(source));

            return ToHashSetCore(source, comparer: null, cancellationToken);
        }

        public static Task<HashSet<TSource>> ToHashSetAsync<TSource>(this IAsyncEnumerable<TSource> source, IEqualityComparer<TSource> comparer, CancellationToken cancellationToken = default)
        {
            if (source == null)
                throw Error.ArgumentNull(nameof(source));

            return ToHashSetCore(source, comparer, cancellationToken);
        }

        private static async Task<HashSet<TSource>> ToHashSetCore<TSource>(IAsyncEnumerable<TSource> source, IEqualityComparer<TSource> comparer, CancellationToken cancellationToken)
        {
            var set = new HashSet<TSource>(comparer);

#if CSHARP8 && AETOR_HAS_CT // CS0656 Missing compiler required member 'System.Collections.Generic.IAsyncEnumerable`1.GetAsyncEnumerator'
            await foreach (TSource item in source.WithCancellation(cancellationToken).ConfigureAwait(false))
            {
                set.Add(item);
            }
#else
            var e = source.GetAsyncEnumerator(cancellationToken);

            try
            {
                while (await e.MoveNextAsync().ConfigureAwait(false))
                {
                    set.Add(e.Current);
                }
            }
            finally
            {
                await e.DisposeAsync().ConfigureAwait(false);
            }
#endif

            return set;
        }
    }
}