Add ToHashSet.

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

@@ -0,0 +1,50 @@
+// 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<HashSet<TSource>> ToHashSet<TSource>(this IAsyncObservable<TSource> source)
+        {
+            if (source == null)
+                throw new ArgumentNullException(nameof(source));
+
+            return Create<HashSet<TSource>>(observer => source.SubscribeAsync(AsyncObserver.ToHashSet(observer)));
+        }
+
+        public static IAsyncObservable<HashSet<TSource>> ToHashSet<TSource>(this IAsyncObservable<TSource> source, IEqualityComparer<TSource> comparer)
+        {
+            if (source == null)
+                throw new ArgumentNullException(nameof(source));
+            if (comparer == null)
+                throw new ArgumentNullException(nameof(comparer));
+
+            return Create<HashSet<TSource>>(observer => source.SubscribeAsync(AsyncObserver.ToHashSet(observer, comparer)));
+        }
+    }
+
+    partial class AsyncObserver
+    {
+        public static IAsyncObserver<TSource> ToHashSet<TSource>(IAsyncObserver<HashSet<TSource>> observer)
+        {
+            if (observer == null)
+                throw new ArgumentNullException(nameof(observer));
+
+            return ToHashSet(observer, EqualityComparer<TSource>.Default);
+        }
+
+        public static IAsyncObserver<TSource> ToHashSet<TSource>(IAsyncObserver<HashSet<TSource>> observer, IEqualityComparer<TSource> comparer)
+        {
+            if (observer == null)
+                throw new ArgumentNullException(nameof(observer));
+            if (comparer == null)
+                throw new ArgumentNullException(nameof(comparer));
+
+            return Aggregate<TSource, HashSet<TSource>>(observer, new HashSet<TSource>(comparer), (set, x) => { set.Add(x); return set; });
+        }
+    }
+}