reactive/Ix.NET/Source/System.Interactive.Async/Defer.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;

namespace System.Linq
{
    public static partial class AsyncEnumerable
    {
        public static IAsyncEnumerable<TSource> Defer<TSource>(Func<IAsyncEnumerable<TSource>> factory)
        {
            if (factory == null)
            {
                throw new ArgumentNullException(nameof(factory));
            }

            return CreateEnumerable(
                () => factory()
                    .GetEnumerator());
        }
    }
}