Adding unsafe observers.

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

@@ -31,5 +31,17 @@ namespace System.Reactive.Linq
 
             return new AsyncObserver<T>(onNextAsync, onErrorAsync, onCompletedAsync);
         }
+
+        internal static IAsyncObserver<T> CreateUnsafe<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 UnsafeAsyncObserver<T>(onNextAsync, onErrorAsync, onCompletedAsync);
+        }
     }
 }

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

@@ -0,0 +1,35 @@
+// 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
+{
+    public class UnsafeAsyncObserver<T> : IAsyncObserver<T>
+    {
+        private readonly Func<T, Task> _onNextAsync;
+        private readonly Func<Exception, Task> _onErrorAsync;
+        private readonly Func<Task> _onCompletedAsync;
+
+        public UnsafeAsyncObserver(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));
+
+            _onNextAsync = onNextAsync;
+            _onErrorAsync = onErrorAsync;
+            _onCompletedAsync = onCompletedAsync;
+        }
+
+        public Task OnCompletedAsync() => _onCompletedAsync();
+
+        public Task OnErrorAsync(Exception error) => _onErrorAsync(error ?? throw new ArgumentNullException(nameof(error)));
+
+        public Task OnNextAsync(T value) => _onNextAsync(value);
+    }
+}