Adding AsyncSubject.Create.

AsyncRx.NET/System.Reactive.Async.Core/System/Reactive/Subjects/AnonymousAsyncSubject.cs

@@ -0,0 +1,28 @@
+// 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.Threading.Tasks;
+
+namespace System.Reactive.Subjects
+{
+    internal sealed class AnonymousAsyncSubject<T> : IAsyncSubject<T>
+    {
+        private readonly IAsyncObserver<T> _observer;
+        private readonly IAsyncObservable<T> _observable;
+
+        public AnonymousAsyncSubject(IAsyncObserver<T> observer, IAsyncObservable<T> observable)
+        {
+            _observer = observer;
+            _observable = observable;
+        }
+
+        public Task OnCompletedAsync() => _observer.OnCompletedAsync();
+
+        public Task OnErrorAsync(Exception error) => _observer.OnErrorAsync(error ?? throw new ArgumentNullException(nameof(error)));
+
+        public Task OnNextAsync(T value) => _observer.OnNextAsync(value);
+
+        public Task<IAsyncDisposable> SubscribeAsync(IAsyncObserver<T> observer) => _observable.SubscribeAsync(observer ?? throw new ArgumentNullException(nameof(observer)));
+    }
+}

AsyncRx.NET/System.Reactive.Async.Core/System/Reactive/Subjects/AsyncSubject.cs

@@ -0,0 +1,19 @@
+// 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. 
+
+namespace System.Reactive.Subjects
+{
+    public static class AsyncSubject
+    {
+        public static IAsyncSubject<T> Create<T>(IAsyncObserver<T> observer, IAsyncObservable<T> observable)
+        {
+            if (observer == null)
+                throw new ArgumentNullException(nameof(observer));
+            if (observable == null)
+                throw new ArgumentNullException(nameof(observable));
+
+            return new AnonymousAsyncSubject<T>(observer, observable);
+        }
+    }
+}