Adding First[OrDefault].

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

@@ -0,0 +1,81 @@
+// 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> First<TSource>(this IAsyncObservable<TSource> source)
+        {
+            if (source == null)
+                throw new ArgumentNullException(nameof(source));
+
+            return Create<TSource>(observer => source.SubscribeAsync(AsyncObserver.First(observer)));
+        }
+
+        public static IAsyncObservable<TSource> First<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.First(observer, predicate)));
+        }
+
+        public static IAsyncObservable<TSource> First<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.First(observer, predicate)));
+        }
+    }
+
+    partial class AsyncObserver
+    {
+        public static IAsyncObserver<TSource> First<TSource>(IAsyncObserver<TSource> observer)
+        {
+            if (observer == null)
+                throw new ArgumentNullException(nameof(observer));
+
+            return Create<TSource>(
+                async x =>
+                {
+                    await observer.OnNextAsync(x).ConfigureAwait(false);
+                    await observer.OnCompletedAsync().ConfigureAwait(false);
+                },
+                observer.OnErrorAsync,
+                async () =>
+                {
+                    await observer.OnErrorAsync(new InvalidOperationException("The sequence is empty.")).ConfigureAwait(false);
+                }
+            );
+        }
+
+        public static IAsyncObserver<TSource> First<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(First(observer), predicate);
+        }
+
+        public static IAsyncObserver<TSource> First<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(First(observer), predicate);
+        }
+    }
+}

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

@@ -0,0 +1,82 @@
+// 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> FirstOrDefault<TSource>(this IAsyncObservable<TSource> source)
+        {
+            if (source == null)
+                throw new ArgumentNullException(nameof(source));
+
+            return Create<TSource>(observer => source.SubscribeAsync(AsyncObserver.FirstOrDefault(observer)));
+        }
+
+        public static IAsyncObservable<TSource> FirstOrDefault<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.FirstOrDefault(observer, predicate)));
+        }
+
+        public static IAsyncObservable<TSource> FirstOrDefault<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.FirstOrDefault(observer, predicate)));
+        }
+    }
+
+    partial class AsyncObserver
+    {
+        public static IAsyncObserver<TSource> FirstOrDefault<TSource>(IAsyncObserver<TSource> observer)
+        {
+            if (observer == null)
+                throw new ArgumentNullException(nameof(observer));
+
+            return Create<TSource>(
+                async x =>
+                {
+                    await observer.OnNextAsync(x).ConfigureAwait(false);
+                    await observer.OnCompletedAsync().ConfigureAwait(false);
+                },
+                observer.OnErrorAsync,
+                async () =>
+                {
+                    await observer.OnNextAsync(default(TSource)).ConfigureAwait(false);
+                    await observer.OnCompletedAsync().ConfigureAwait(false);
+                }
+            );
+        }
+
+        public static IAsyncObserver<TSource> FirstOrDefault<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(FirstOrDefault(observer), predicate);
+        }
+
+        public static IAsyncObserver<TSource> FirstOrDefault<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(FirstOrDefault(observer), predicate);
+        }
+    }
+}