Adding TakeLast.

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

@@ -0,0 +1,150 @@
+// 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;
+using System.Reactive.Concurrency;
+using System.Threading.Tasks;
+
+namespace System.Reactive.Linq
+{
+    partial class AsyncObservable
+    {
+        public static IAsyncObservable<TSource> TakeLast<TSource>(this IAsyncObservable<TSource> source, int count)
+        {
+            if (source == null)
+                throw new ArgumentNullException(nameof(source));
+            if (count < 0)
+                throw new ArgumentOutOfRangeException(nameof(count));
+
+            if (count == 0)
+            {
+                return Empty<TSource>();
+            }
+
+            return Create<TSource>(observer => source.SubscribeAsync(AsyncObserver.TakeLast(observer, count)));
+        }
+
+        public static IAsyncObservable<TSource> TakeLast<TSource>(this IAsyncObservable<TSource> source, int count, IAsyncScheduler scheduler)
+        {
+            if (source == null)
+                throw new ArgumentNullException(nameof(source));
+            if (count < 0)
+                throw new ArgumentOutOfRangeException(nameof(count));
+            if (scheduler == null)
+                throw new ArgumentNullException(nameof(scheduler));
+
+            if (count == 0)
+            {
+                return Empty<TSource>();
+            }
+
+            return Create<TSource>(observer => source.SubscribeAsync(AsyncObserver.TakeLast(observer, count, scheduler)));
+        }
+
+        public static IAsyncObservable<TSource> TakeLast<TSource>(this IAsyncObservable<TSource> source, TimeSpan duration)
+        {
+            if (source == null)
+                throw new ArgumentNullException(nameof(source));
+            if (duration < TimeSpan.Zero)
+                throw new ArgumentOutOfRangeException(nameof(duration));
+
+            if (duration == TimeSpan.Zero)
+            {
+                return Empty<TSource>();
+            }
+
+            return Create<TSource>(observer => source.SubscribeAsync(AsyncObserver.TakeLast(observer, duration)));
+        }
+
+        public static IAsyncObservable<TSource> TakeLast<TSource>(this IAsyncObservable<TSource> source, TimeSpan duration, IAsyncScheduler scheduler)
+        {
+            if (source == null)
+                throw new ArgumentNullException(nameof(source));
+            if (duration < TimeSpan.Zero)
+                throw new ArgumentOutOfRangeException(nameof(duration));
+            if (scheduler == null)
+                throw new ArgumentNullException(nameof(scheduler));
+
+            if (duration == TimeSpan.Zero)
+            {
+                return Empty<TSource>();
+            }
+
+            return Create<TSource>(observer => source.SubscribeAsync(AsyncObserver.TakeLast(observer, duration, scheduler)));
+        }
+    }
+
+    partial class AsyncObserver
+    {
+        public static IAsyncObserver<TSource> TakeLast<TSource>(IAsyncObserver<TSource> observer, int count)
+        {
+            if (observer == null)
+                throw new ArgumentNullException(nameof(observer));
+            if (count <= 0)
+                throw new ArgumentOutOfRangeException(nameof(count));
+
+            var queue = new Queue<TSource>();
+
+            return Create<TSource>(
+                x =>
+                {
+                    queue.Enqueue(x);
+
+                    if (queue.Count > count)
+                    {
+                        queue.Dequeue();
+                    }
+
+                    return Task.CompletedTask;
+                },
+                observer.OnErrorAsync,
+                async () =>
+                {
+                    var n = queue.Count;
+
+                    while (queue.Count > 0)
+                    {
+                        await observer.OnNextAsync(queue.Dequeue()).ConfigureAwait(false);
+                    }
+
+                    await observer.OnCompletedAsync().ConfigureAwait(false);
+                }
+            );
+        }
+
+        public static IAsyncObserver<TSource> TakeLast<TSource>(IAsyncObserver<TSource> observer, int count, IAsyncScheduler scheduler)
+        {
+            if (observer == null)
+                throw new ArgumentNullException(nameof(observer));
+            if (count <= 0)
+                throw new ArgumentOutOfRangeException(nameof(count));
+            if (scheduler == null)
+                throw new ArgumentNullException(nameof(scheduler));
+
+            throw new NotImplementedException();
+        }
+
+        public static IAsyncObserver<TSource> TakeLast<TSource>(IAsyncObserver<TSource> observer, TimeSpan duration)
+        {
+            if (observer == null)
+                throw new ArgumentNullException(nameof(observer));
+            if (duration < TimeSpan.Zero)
+                throw new ArgumentOutOfRangeException(nameof(duration));
+
+            throw new NotImplementedException();
+        }
+
+        public static IAsyncObserver<TSource> TakeLast<TSource>(IAsyncObserver<TSource> observer, TimeSpan duration, IAsyncScheduler scheduler)
+        {
+            if (observer == null)
+                throw new ArgumentNullException(nameof(observer));
+            if (duration < TimeSpan.Zero)
+                throw new ArgumentOutOfRangeException(nameof(duration));
+            if (scheduler == null)
+                throw new ArgumentNullException(nameof(scheduler));
+
+            throw new NotImplementedException();
+        }
+    }
+}

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

@@ -3,7 +3,6 @@
 // See the LICENSE file in the project root for more information. 
 
 using System.Collections.Generic;
-using System.Linq;
 using System.Reactive.Concurrency;
 using System.Threading.Tasks;
 
@@ -85,7 +84,16 @@ namespace System.Reactive.Linq
                 observer.OnErrorAsync,
                 async () =>
                 {
-                    await observer.OnNextAsync(queue.ToList()).ConfigureAwait(false);
+                    var n = queue.Count;
+
+                    var res = new List<TSource>(n);
+
+                    while (queue.Count > 0)
+                    {
+                        res.Add(queue.Dequeue());
+                    }
+
+                    await observer.OnNextAsync(res).ConfigureAwait(false);
                     await observer.OnCompletedAsync().ConfigureAwait(false);
                 }
             );