reactive/Ix.NET/Source/System.Interactive.Async/Zip.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;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

namespace System.Linq
{
    public static partial class AsyncEnumerable
    {
        public static IAsyncEnumerable<TResult> Zip<TFirst, TSecond, TResult>(this IAsyncEnumerable<TFirst> first, IAsyncEnumerable<TSecond> second, Func<TFirst, TSecond, TResult> selector)
        {
            if (first == null)
                throw new ArgumentNullException(nameof(first));
            if (second == null)
                throw new ArgumentNullException(nameof(second));
            if (selector == null)
                throw new ArgumentNullException(nameof(selector));

            return CreateEnumerable(
                () =>
                {
                    var e1 = first.GetEnumerator();
                    var e2 = second.GetEnumerator();
                    var current = default(TResult);

                    var cts = new CancellationTokenDisposable();
                    var d = Disposable.Create(cts, e1, e2);

                    return CreateEnumerator(
                        ct => e1.MoveNext(cts.Token)
                                .Zip(e2.MoveNext(cts.Token),
                                     (f, s) =>
                                     {
                                         var result = f && s;
                                         if (result)
                                             current = selector(e1.Current, e2.Current);
                                         return result;
                                     }),
                        () => current,
                        d.Dispose
                    );
                });
        }
    }
}