Skeleton for AsyncObserver.Create.

AsyncRx.NET/System.Reactive.Async/System/Reactive/Linq/AsyncObserver.cs

@@ -2,9 +2,51 @@
 // 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.Linq
 {
     public static class AsyncObserver
     {
+        public static IAsyncObserver<T> Create<T>(Func<T, Task> onNextAsync, Func<Exception, Task> onErrorAsync, Func<Task> onCompletedAsync)
+        {
+            if (onNextAsync == null)
+                throw new ArgumentNullException(nameof(onNextAsync));
+            if (onErrorAsync == null)
+                throw new ArgumentNullException(nameof(onErrorAsync));
+            if (onCompletedAsync == null)
+                throw new ArgumentNullException(nameof(onCompletedAsync));
+
+            return new AnonymousAsyncObserver<T>(onNextAsync, onErrorAsync, onCompletedAsync);
+        }
+
+        private sealed class AnonymousAsyncObserver<T> : IAsyncObserver<T>
+        {
+            private readonly Func<T, Task> _onNextAsync;
+            private readonly Func<Exception, Task> _onErrorAsync;
+            private readonly Func<Task> _onCompletedAsync;
+
+            public AnonymousAsyncObserver(Func<T, Task> onNextAsync, Func<Exception, Task> onErrorAsync, Func<Task> onCompletedAsync)
+            {
+                _onNextAsync = onNextAsync;
+                _onErrorAsync = onErrorAsync;
+                _onCompletedAsync = onCompletedAsync;
+            }
+
+            public Task OnCompletedAsync()
+            {
+                throw new NotImplementedException();
+            }
+
+            public Task OnErrorAsync(Exception error)
+            {
+                throw new NotImplementedException();
+            }
+
+            public Task OnNextAsync(T value)
+            {
+                throw new NotImplementedException();
+            }
+        }
     }
 }