Adding some placeholder overloads with IAsyncScheduler.

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

@@ -2,6 +2,8 @@
 // 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.Concurrency;
+
 namespace System.Reactive.Linq
 {
     partial class AsyncObservable
@@ -13,6 +15,16 @@ namespace System.Reactive.Linq
 
             return Create<TSource>(observer => source.SubscribeAsync(AsyncObserver.Append(observer, element)));
         }
+
+        public static IAsyncObservable<TSource> Append<TSource>(this IAsyncObservable<TSource> source, TSource element, IAsyncScheduler scheduler)
+        {
+            if (source == null)
+                throw new ArgumentNullException(nameof(source));
+            if (scheduler == null)
+                throw new ArgumentNullException(nameof(scheduler));
+
+            return Create<TSource>(observer => source.SubscribeAsync(AsyncObserver.Append(observer, element, scheduler)));
+        }
     }
 
     partial class AsyncObserver
@@ -32,5 +44,15 @@ namespace System.Reactive.Linq
                 }
             );
         }
+
+        public static IAsyncObserver<TSource> Append<TSource>(IAsyncObserver<TSource> observer, TSource element, IAsyncScheduler scheduler)
+        {
+            if (observer == null)
+                throw new ArgumentNullException(nameof(observer));
+            if (scheduler == null)
+                throw new ArgumentNullException(nameof(scheduler));
+
+            throw new NotImplementedException();
+        }
     }
 }

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

@@ -2,6 +2,7 @@
 // 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.Concurrency;
 using System.Reactive.Disposables;
 
 namespace System.Reactive.Linq
@@ -16,5 +17,13 @@ namespace System.Reactive.Linq
                 return AsyncDisposable.Nop;
             });
         }
+
+        public static IAsyncObservable<TSource> Empty<TSource>(IAsyncScheduler scheduler)
+        {
+            if (scheduler == null)
+                throw new ArgumentNullException(nameof(scheduler));
+
+            throw new NotImplementedException();
+        }
     }
 }

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

@@ -2,6 +2,7 @@
 // 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.Concurrency;
 using System.Reactive.Disposables;
 
 namespace System.Reactive.Linq
@@ -17,5 +18,13 @@ namespace System.Reactive.Linq
                 return AsyncDisposable.Nop;
             });
         }
+
+        public static IAsyncObservable<TSource> Return<TSource>(TSource value, IAsyncScheduler scheduler)
+        {
+            if (scheduler == null)
+                throw new ArgumentNullException(nameof(scheduler));
+
+            throw new NotImplementedException();
+        }
     }
 }

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

@@ -2,6 +2,7 @@
 // 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.Concurrency;
 using System.Reactive.Disposables;
 
 namespace System.Reactive.Linq
@@ -19,5 +20,15 @@ namespace System.Reactive.Linq
                 return AsyncDisposable.Nop;
             });
         }
+
+        public static IAsyncObservable<TSource> Throw<TSource>(Exception error, IAsyncScheduler scheduler)
+        {
+            if (error == null)
+                throw new ArgumentNullException(nameof(error));
+            if (scheduler == null)
+                throw new ArgumentNullException(nameof(scheduler));
+
+            throw new NotImplementedException();
+        }
     }
 }