Adding Distinct.

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

@@ -0,0 +1,74 @@
+// 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.Collections.Generic;
+
+namespace System.Reactive.Linq
+{
+    partial class AsyncObservable
+    {
+        public static IAsyncObservable<TSource> Distinct<TSource>(IAsyncObservable<TSource> source)
+        {
+            if (source == null)
+                throw new ArgumentNullException(nameof(source));
+
+            return Create<TSource>(observer => source.SubscribeAsync(AsyncObserver.Distinct(observer)));
+        }
+
+        public static IAsyncObservable<TSource> Distinct<TSource>(IAsyncObservable<TSource> source, IEqualityComparer<TSource> comparer)
+        {
+            if (source == null)
+                throw new ArgumentNullException(nameof(source));
+            if (comparer == null)
+                throw new ArgumentNullException(nameof(comparer));
+
+            return Create<TSource>(observer => source.SubscribeAsync(AsyncObserver.Distinct(observer, comparer)));
+        }
+    }
+
+    partial class AsyncObserver
+    {
+        public static IAsyncObserver<TSource> Distinct<TSource>(IAsyncObserver<TSource> observer)
+        {
+            if (observer == null)
+                throw new ArgumentNullException(nameof(observer));
+
+            return Distinct(observer, EqualityComparer<TSource>.Default);
+        }
+
+        public static IAsyncObserver<TSource> Distinct<TSource>(IAsyncObserver<TSource> observer, IEqualityComparer<TSource> comparer)
+        {
+            if (observer == null)
+                throw new ArgumentNullException(nameof(observer));
+            if (comparer == null)
+                throw new ArgumentNullException(nameof(comparer));
+
+            var set = new HashSet<TSource>(comparer);
+
+            return Create<TSource>(
+                async x =>
+                {
+                    var added = false;
+
+                    try
+                    {
+                        added = set.Add(x);
+                    }
+                    catch (Exception ex)
+                    {
+                        await observer.OnErrorAsync(ex).ConfigureAwait(false);
+                        return;
+                    }
+
+                    if (added)
+                    {
+                        await observer.OnNextAsync(x).ConfigureAwait(false);
+                    }
+                },
+                observer.OnErrorAsync,
+                observer.OnCompletedAsync
+            );
+        }
+    }
+}