Adding StartAsync.

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

@@ -0,0 +1,120 @@
+// 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.Concurrency;
+using System.Reactive.Disposables;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace System.Reactive.Linq
+{
+    partial class AsyncObservable
+    {
+        public static IAsyncObservable<TSource> StartAsync<TSource>(Func<Task<TSource>> functionAsync) => StartAsync(functionAsync, ImmediateAsyncScheduler.Instance);
+
+        public static IAsyncObservable<TSource> StartAsync<TSource>(Func<Task<TSource>> functionAsync, IAsyncScheduler scheduler)
+        {
+            if (functionAsync == null)
+                throw new ArgumentNullException(nameof(functionAsync));
+            if (scheduler == null)
+                throw new ArgumentNullException(nameof(scheduler));
+
+            var task = default(Task<TSource>);
+
+            try
+            {
+                task = functionAsync();
+            }
+            catch (Exception ex)
+            {
+                return Throw<TSource>(ex);
+            }
+
+            return task.ToAsyncObservable(scheduler);
+        }
+
+        public static IAsyncObservable<TSource> StartAsync<TSource>(Func<CancellationToken, Task<TSource>> functionAsync) => StartAsync(functionAsync, ImmediateAsyncScheduler.Instance);
+
+        public static IAsyncObservable<TSource> StartAsync<TSource>(Func<CancellationToken, Task<TSource>> functionAsync, IAsyncScheduler scheduler)
+        {
+            if (functionAsync == null)
+                throw new ArgumentNullException(nameof(functionAsync));
+            if (scheduler == null)
+                throw new ArgumentNullException(nameof(scheduler));
+
+            var cancel = new CancellationAsyncDisposable();
+
+            var task = default(Task<TSource>);
+
+            try
+            {
+                task = functionAsync(cancel.Token);
+            }
+            catch (Exception ex)
+            {
+                return Throw<TSource>(ex);
+            }
+
+            return Create<TSource>(async observer =>
+            {
+                var subscription = await task.ToAsyncObservable(scheduler).SubscribeAsync(observer);
+
+                return StableCompositeAsyncDisposable.Create(cancel, subscription);
+            });
+        }
+
+        public static IAsyncObservable<Unit> StartAsync(Func<Task> actionAsync) => StartAsync(actionAsync, ImmediateAsyncScheduler.Instance);
+
+        public static IAsyncObservable<Unit> StartAsync(Func<Task> actionAsync, IAsyncScheduler scheduler)
+        {
+            if (actionAsync == null)
+                throw new ArgumentNullException(nameof(actionAsync));
+            if (scheduler == null)
+                throw new ArgumentNullException(nameof(scheduler));
+
+            var task = default(Task);
+
+            try
+            {
+                task = actionAsync();
+            }
+            catch (Exception ex)
+            {
+                return Throw<Unit>(ex);
+            }
+
+            return task.ToAsyncObservable(scheduler);
+        }
+
+        public static IAsyncObservable<Unit> StartAsync(Func<CancellationToken, Task> actionAsync) => StartAsync(actionAsync, ImmediateAsyncScheduler.Instance);
+
+        public static IAsyncObservable<Unit> StartAsync(Func<CancellationToken, Task> actionAsync, IAsyncScheduler scheduler)
+        {
+            if (actionAsync == null)
+                throw new ArgumentNullException(nameof(actionAsync));
+            if (scheduler == null)
+                throw new ArgumentNullException(nameof(scheduler));
+
+            var cancel = new CancellationAsyncDisposable();
+
+            var task = default(Task);
+
+            try
+            {
+                task = actionAsync(cancel.Token);
+            }
+            catch (Exception ex)
+            {
+                return Throw<Unit>(ex);
+            }
+
+            return Create<Unit>(async observer =>
+            {
+                var subscription = await task.ToAsyncObservable(scheduler).SubscribeAsync(observer);
+
+                return StableCompositeAsyncDisposable.Create(cancel, subscription);
+            });
+        }
+    }
+}