Adding Single[OrDefault].

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

@@ -0,0 +1,98 @@
+// 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.Linq
+{
+    partial class AsyncObservable
+    {
+        public static IAsyncObservable<TSource> Single<TSource>(this IAsyncObservable<TSource> source)
+        {
+            if (source == null)
+                throw new ArgumentNullException(nameof(source));
+
+            return Create<TSource>(observer => source.SubscribeAsync(AsyncObserver.Single(observer)));
+        }
+
+        public static IAsyncObservable<TSource> Single<TSource>(this IAsyncObservable<TSource> source, Func<TSource, bool> predicate)
+        {
+            if (source == null)
+                throw new ArgumentNullException(nameof(source));
+            if (predicate == null)
+                throw new ArgumentNullException(nameof(predicate));
+
+            return Create<TSource>(observer => source.SubscribeAsync(AsyncObserver.Single(observer, predicate)));
+        }
+
+        public static IAsyncObservable<TSource> Single<TSource>(this IAsyncObservable<TSource> source, Func<TSource, Task<bool>> predicate)
+        {
+            if (source == null)
+                throw new ArgumentNullException(nameof(source));
+            if (predicate == null)
+                throw new ArgumentNullException(nameof(predicate));
+
+            return Create<TSource>(observer => source.SubscribeAsync(AsyncObserver.Single(observer, predicate)));
+        }
+    }
+
+    partial class AsyncObserver
+    {
+        public static IAsyncObserver<TSource> Single<TSource>(IAsyncObserver<TSource> observer)
+        {
+            if (observer == null)
+                throw new ArgumentNullException(nameof(observer));
+
+            var hasValue = false;
+            var value = default(TSource);
+
+            return Create<TSource>(
+                async x =>
+                {
+                    if (hasValue)
+                    {
+                        await observer.OnErrorAsync(new InvalidOperationException("The sequence contains more than one element.")).ConfigureAwait(false);
+                        return;
+                    }
+
+                    hasValue = true;
+                    value = x;
+                },
+                observer.OnErrorAsync,
+                async () =>
+                {
+                    if (!hasValue)
+                    {
+                        await observer.OnErrorAsync(new InvalidOperationException("The sequence is empty.")).ConfigureAwait(false);
+                    }
+                    else
+                    {
+                        await observer.OnNextAsync(value).ConfigureAwait(false);
+                        await observer.OnCompletedAsync().ConfigureAwait(false);
+                    }
+                }
+            );
+        }
+
+        public static IAsyncObserver<TSource> Single<TSource>(IAsyncObserver<TSource> observer, Func<TSource, bool> predicate)
+        {
+            if (observer == null)
+                throw new ArgumentNullException(nameof(observer));
+            if (predicate == null)
+                throw new ArgumentNullException(nameof(predicate));
+
+            return Where(Single(observer), predicate);
+        }
+
+        public static IAsyncObserver<TSource> Single<TSource>(IAsyncObserver<TSource> observer, Func<TSource, Task<bool>> predicate)
+        {
+            if (observer == null)
+                throw new ArgumentNullException(nameof(observer));
+            if (predicate == null)
+                throw new ArgumentNullException(nameof(predicate));
+
+            return Where(Single(observer), predicate);
+        }
+    }
+}

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

@@ -0,0 +1,91 @@
+// 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.Linq
+{
+    partial class AsyncObservable
+    {
+        public static IAsyncObservable<TSource> SingleOrDefault<TSource>(this IAsyncObservable<TSource> source)
+        {
+            if (source == null)
+                throw new ArgumentNullException(nameof(source));
+
+            return Create<TSource>(observer => source.SubscribeAsync(AsyncObserver.SingleOrDefault(observer)));
+        }
+
+        public static IAsyncObservable<TSource> SingleOrDefault<TSource>(this IAsyncObservable<TSource> source, Func<TSource, bool> predicate)
+        {
+            if (source == null)
+                throw new ArgumentNullException(nameof(source));
+            if (predicate == null)
+                throw new ArgumentNullException(nameof(predicate));
+
+            return Create<TSource>(observer => source.SubscribeAsync(AsyncObserver.SingleOrDefault(observer, predicate)));
+        }
+
+        public static IAsyncObservable<TSource> SingleOrDefault<TSource>(this IAsyncObservable<TSource> source, Func<TSource, Task<bool>> predicate)
+        {
+            if (source == null)
+                throw new ArgumentNullException(nameof(source));
+            if (predicate == null)
+                throw new ArgumentNullException(nameof(predicate));
+
+            return Create<TSource>(observer => source.SubscribeAsync(AsyncObserver.SingleOrDefault(observer, predicate)));
+        }
+    }
+
+    partial class AsyncObserver
+    {
+        public static IAsyncObserver<TSource> SingleOrDefault<TSource>(IAsyncObserver<TSource> observer)
+        {
+            if (observer == null)
+                throw new ArgumentNullException(nameof(observer));
+
+            var hasValue = false;
+            var value = default(TSource);
+
+            return Create<TSource>(
+                async x =>
+                {
+                    if (hasValue)
+                    {
+                        await observer.OnErrorAsync(new InvalidOperationException("The sequence contains more than one element.")).ConfigureAwait(false);
+                        return;
+                    }
+
+                    hasValue = true;
+                    value = x;
+                },
+                observer.OnErrorAsync,
+                async () =>
+                {
+                    await observer.OnNextAsync(hasValue ? value : default(TSource)).ConfigureAwait(false);
+                    await observer.OnCompletedAsync().ConfigureAwait(false);
+                }
+            );
+        }
+
+        public static IAsyncObserver<TSource> SingleOrDefault<TSource>(IAsyncObserver<TSource> observer, Func<TSource, bool> predicate)
+        {
+            if (observer == null)
+                throw new ArgumentNullException(nameof(observer));
+            if (predicate == null)
+                throw new ArgumentNullException(nameof(predicate));
+
+            return Where(SingleOrDefault(observer), predicate);
+        }
+
+        public static IAsyncObserver<TSource> SingleOrDefault<TSource>(IAsyncObserver<TSource> observer, Func<TSource, Task<bool>> predicate)
+        {
+            if (observer == null)
+                throw new ArgumentNullException(nameof(observer));
+            if (predicate == null)
+                throw new ArgumentNullException(nameof(predicate));
+
+            return Where(SingleOrDefault(observer), predicate);
+        }
+    }
+}