// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
 
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;
 
namespace System.Linq
{
    public static partial class AsyncEnumerable
    {
        /// <summary>
        /// Returns an empty <see cref="IAsyncEnumerable{T}"/> that has the specified type argument.
        /// </summary>
        /// <typeparam name="TResult">The type of the elements of the sequence.</typeparam>
        /// <returns>An empty <see cref="IAsyncEnumerable{T}"/> whose type argument is <typeparamref name="TResult"/>.</returns>
        public static IAsyncEnumerable<TResult> Empty<TResult>() => EmptyAsyncEnumerable<TResult>.Instance;
 
        private sealed class EmptyAsyncEnumerable<TResult> : IAsyncEnumerable<TResult>, IAsyncEnumerator<TResult>
        {
            public static EmptyAsyncEnumerable<TResult> Instance { get; } = new EmptyAsyncEnumerable<TResult>();
 
            public IAsyncEnumerator<TResult> GetAsyncEnumerator(CancellationToken cancellationToken = default) => this;
 
            public ValueTask<bool> MoveNextAsync() => default;
 
            public TResult Current => default!;
 
            public ValueTask DisposeAsync() => default;
        }
    }
}