Adding PublishLast.

AsyncRx.NET/System.Reactive.Async/System/Reactive/Linq/Operators/PublishLast.cs

@@ -0,0 +1,34 @@
+// 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.Reactive.Subjects;
+using System.Threading.Tasks;
+
+namespace System.Reactive.Linq
+{
+    // REVIEW: Expose PublishLast using ConcurrentAsyncAsyncSubject<T> underneath.
+
+    partial class AsyncObservable
+    {
+        public static IAsyncObservable<TResult> PublishLast<TSource, TResult>(this IAsyncObservable<TSource> source, Func<IAsyncObservable<TSource>, IAsyncObservable<TResult>> selector)
+        {
+            if (source == null)
+                throw new ArgumentNullException(nameof(source));
+            if (selector == null)
+                throw new ArgumentNullException(nameof(selector));
+
+            return Multicast(source, () => new SequentialAsyncAsyncSubject<TSource>(), selector);
+        }
+
+        public static IAsyncObservable<TResult> PublishLast<TSource, TResult>(this IAsyncObservable<TSource> source, Func<IAsyncObservable<TSource>, Task<IAsyncObservable<TResult>>> selector)
+        {
+            if (source == null)
+                throw new ArgumentNullException(nameof(source));
+            if (selector == null)
+                throw new ArgumentNullException(nameof(selector));
+
+            return Multicast(source, () => Task.FromResult<IAsyncSubject<TSource, TSource>>(new SequentialAsyncAsyncSubject<TSource>()), selector);
+        }
+    }
+}