reactive/Ix.NET/Source/System.Linq.Async/System/Linq/Operators/ToList.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<List<TSource>> ToList<TSource>(this IAsyncEnumerable<TSource> source)
        {
            if (source == null)
                throw new ArgumentNullException(nameof(source));

            return ToList(source, CancellationToken.None);
        }

        public static Task<List<TSource>> ToList<TSource>(this IAsyncEnumerable<TSource> source, CancellationToken cancellationToken)
        {
            if (source == null)
                throw new ArgumentNullException(nameof(source));

            if (source is IIListProvider<TSource> listProvider)
                return listProvider.ToListAsync(cancellationToken);

            return source.Aggregate(
                new List<TSource>(),
                (list, x) =>
                {
                    list.Add(x);
                    return list;
                },
                cancellationToken
            );
        }
    }
}