Adding TimeInterval.

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

@@ -0,0 +1,43 @@
+// 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;
+
+namespace System.Reactive.Linq
+{
+    partial class AsyncObservable
+    {
+        public static IAsyncObservable<TimeInterval<TSource>> TimeInterval<TSource>(this IAsyncObservable<TSource> source, IClock clock)
+        {
+            if (source == null)
+                throw new ArgumentNullException(nameof(source));
+            if (clock == null)
+                throw new ArgumentNullException(nameof(clock));
+
+            return Create<TimeInterval<TSource>>(observer => source.SubscribeAsync(AsyncObserver.TimeInterval(observer, clock)));
+        }
+    }
+
+    partial class AsyncObserver
+    {
+        public static IAsyncObserver<TSource> TimeInterval<TSource>(IAsyncObserver<TimeInterval<TSource>> observer, IClock clock)
+        {
+            if (observer == null)
+                throw new ArgumentNullException(nameof(observer));
+            if (clock == null)
+                throw new ArgumentNullException(nameof(clock));
+
+            var last = clock.Now;
+
+            return Select<TSource, TimeInterval<TSource>>(observer, x =>
+            {
+                var now = clock.Now;
+                var interval = now - last;
+                last = now;
+
+                return new TimeInterval<TSource>(x, interval);
+            });
+        }
+    }
+}