Splitting Skip and Take operators.

Ix.NET/Source/System.Interactive.Async/Skip.cs

@@ -30,66 +30,6 @@ namespace System.Linq
             return new SkipAsyncIterator<TSource>(source, count);
         }
 
-        public static IAsyncEnumerable<TSource> SkipLast<TSource>(this IAsyncEnumerable<TSource> source, int count)
-        {
-            if (source == null)
-                throw new ArgumentNullException(nameof(source));
-
-            if (count <= 0)
-            {
-                // Return source if not actually skipping, but only if it's a type from here, to avoid
-                // issues if collections are used as keys or otherwise must not be aliased.
-                if (source is AsyncIterator<TSource>)
-                {
-                    return source;
-                }
-
-                count = 0;
-            }
-
-            return new SkipLastAsyncIterator<TSource>(source, count);
-        }
-
-        public static IAsyncEnumerable<TSource> SkipWhile<TSource>(this IAsyncEnumerable<TSource> source, Func<TSource, bool> predicate)
-        {
-            if (source == null)
-                throw new ArgumentNullException(nameof(source));
-            if (predicate == null)
-                throw new ArgumentNullException(nameof(predicate));
-
-            return new SkipWhileAsyncIterator<TSource>(source, predicate);
-        }
-
-        public static IAsyncEnumerable<TSource> SkipWhile<TSource>(this IAsyncEnumerable<TSource> source, Func<TSource, int, bool> predicate)
-        {
-            if (source == null)
-                throw new ArgumentNullException(nameof(source));
-            if (predicate == null)
-                throw new ArgumentNullException(nameof(predicate));
-
-            return new SkipWhileWithIndexAsyncIterator<TSource>(source, predicate);
-        }
-
-        public static IAsyncEnumerable<TSource> SkipWhile<TSource>(this IAsyncEnumerable<TSource> source, Func<TSource, Task<bool>> predicate)
-        {
-            if (source == null)
-                throw new ArgumentNullException(nameof(source));
-            if (predicate == null)
-                throw new ArgumentNullException(nameof(predicate));
-
-            return new SkipWhileAsyncIteratorWithTask<TSource>(source, predicate);
-        }
-
-        public static IAsyncEnumerable<TSource> SkipWhile<TSource>(this IAsyncEnumerable<TSource> source, Func<TSource, int, Task<bool>> predicate)
-        {
-            if (source == null)
-                throw new ArgumentNullException(nameof(source));
-            if (predicate == null)
-                throw new ArgumentNullException(nameof(predicate));
-
-            return new SkipWhileWithIndexAsyncIteratorWithTask<TSource>(source, predicate);
-        }
-
         private sealed class SkipAsyncIterator<TSource> : AsyncIterator<TSource>
         {
             private readonly int count;
@@ -158,391 +98,5 @@ namespace System.Linq
                 return false;
             }
         }
-
-        private sealed class SkipLastAsyncIterator<TSource> : AsyncIterator<TSource>
-        {
-            private readonly int count;
-            private readonly IAsyncEnumerable<TSource> source;
-
-            private IAsyncEnumerator<TSource> enumerator;
-            private Queue<TSource> queue;
-
-            public SkipLastAsyncIterator(IAsyncEnumerable<TSource> source, int count)
-            {
-                Debug.Assert(source != null);
-
-                this.source = source;
-                this.count = count;
-            }
-
-            public override AsyncIterator<TSource> Clone()
-            {
-                return new SkipLastAsyncIterator<TSource>(source, count);
-            }
-
-            public override async Task DisposeAsync()
-            {
-                if (enumerator != null)
-                {
-                    await enumerator.DisposeAsync().ConfigureAwait(false);
-                    enumerator = null;
-                }
-
-                queue = null; // release the memory
-
-                await base.DisposeAsync().ConfigureAwait(false);
-            }
-
-
-            protected override async Task<bool> MoveNextCore()
-            {
-                switch (state)
-                {
-                    case AsyncIteratorState.Allocated:
-                        enumerator = source.GetAsyncEnumerator();
-                        queue = new Queue<TSource>();
-
-                        state = AsyncIteratorState.Iterating;
-                        goto case AsyncIteratorState.Iterating;
-
-
-                    case AsyncIteratorState.Iterating:
-                        while (await enumerator.MoveNextAsync().ConfigureAwait(false))
-                        {
-                            var item = enumerator.Current;
-                            queue.Enqueue(item);
-
-                            if (queue.Count > count)
-                            {
-                                current = queue.Dequeue();
-                                return true;
-                            }
-                        }
-
-                        break;
-                }
-
-                await DisposeAsync().ConfigureAwait(false);
-                return false;
-            }
-        }
-
-        private sealed class SkipWhileAsyncIterator<TSource> : AsyncIterator<TSource>
-        {
-            private readonly Func<TSource, bool> predicate;
-            private readonly IAsyncEnumerable<TSource> source;
-
-            private bool doMoveNext;
-            private IAsyncEnumerator<TSource> enumerator;
-
-            public SkipWhileAsyncIterator(IAsyncEnumerable<TSource> source, Func<TSource, bool> predicate)
-            {
-                Debug.Assert(predicate != null);
-                Debug.Assert(source != null);
-
-                this.source = source;
-                this.predicate = predicate;
-            }
-
-            public override AsyncIterator<TSource> Clone()
-            {
-                return new SkipWhileAsyncIterator<TSource>(source, predicate);
-            }
-
-            public override async Task DisposeAsync()
-            {
-                if (enumerator != null)
-                {
-                    await enumerator.DisposeAsync().ConfigureAwait(false);
-                    enumerator = null;
-                }
-
-                await base.DisposeAsync().ConfigureAwait(false);
-            }
-
-            protected override async Task<bool> MoveNextCore()
-            {
-                switch (state)
-                {
-                    case AsyncIteratorState.Allocated:
-                        enumerator = source.GetAsyncEnumerator();
-
-                        // skip elements as requested
-                        while (await enumerator.MoveNextAsync().ConfigureAwait(false))
-                        {
-                            var element = enumerator.Current;
-                            if (!predicate(element))
-                            {
-                                doMoveNext = false;
-                                state = AsyncIteratorState.Iterating;
-                                goto case AsyncIteratorState.Iterating;
-                            }
-                        }
-
-                        break;
-
-                    case AsyncIteratorState.Iterating:
-                        if (doMoveNext && await enumerator.MoveNextAsync().ConfigureAwait(false))
-                        {
-                            current = enumerator.Current;
-                            return true;
-                        }
-
-                        if (!doMoveNext)
-                        {
-                            current = enumerator.Current;
-                            doMoveNext = true;
-                            return true;
-                        }
-
-                        break;
-                }
-
-                await DisposeAsync().ConfigureAwait(false);
-                return false;
-            }
-        }
-
-        private sealed class SkipWhileWithIndexAsyncIterator<TSource> : AsyncIterator<TSource>
-        {
-            private readonly Func<TSource, int, bool> predicate;
-            private readonly IAsyncEnumerable<TSource> source;
-
-            private bool doMoveNext;
-            private IAsyncEnumerator<TSource> enumerator;
-            private int index;
-
-            public SkipWhileWithIndexAsyncIterator(IAsyncEnumerable<TSource> source, Func<TSource, int, bool> predicate)
-            {
-                Debug.Assert(predicate != null);
-                Debug.Assert(source != null);
-
-                this.source = source;
-                this.predicate = predicate;
-            }
-
-            public override AsyncIterator<TSource> Clone()
-            {
-                return new SkipWhileWithIndexAsyncIterator<TSource>(source, predicate);
-            }
-
-            public override async Task DisposeAsync()
-            {
-                if (enumerator != null)
-                {
-                    await enumerator.DisposeAsync().ConfigureAwait(false);
-                    enumerator = null;
-                }
-
-                await base.DisposeAsync().ConfigureAwait(false);
-            }
-
-            protected override async Task<bool> MoveNextCore()
-            {
-                switch (state)
-                {
-                    case AsyncIteratorState.Allocated:
-                        enumerator = source.GetAsyncEnumerator();
-                        index = -1;
-
-                        // skip elements as requested
-                        while (await enumerator.MoveNextAsync().ConfigureAwait(false))
-                        {
-                            checked
-                            {
-                                index++;
-                            }
-
-                            var element = enumerator.Current;
-                            if (!predicate(element, index))
-                            {
-                                doMoveNext = false;
-                                state = AsyncIteratorState.Iterating;
-                                goto case AsyncIteratorState.Iterating;
-                            }
-                        }
-
-                        break;
-
-                    case AsyncIteratorState.Iterating:
-                        if (doMoveNext && await enumerator.MoveNextAsync().ConfigureAwait(false))
-                        {
-                            current = enumerator.Current;
-                            return true;
-                        }
-
-                        if (!doMoveNext)
-                        {
-                            current = enumerator.Current;
-                            doMoveNext = true;
-                            return true;
-                        }
-
-                        break;
-                }
-
-                await DisposeAsync().ConfigureAwait(false);
-                return false;
-            }
-        }
-
-        private sealed class SkipWhileAsyncIteratorWithTask<TSource> : AsyncIterator<TSource>
-        {
-            private readonly Func<TSource, Task<bool>> predicate;
-            private readonly IAsyncEnumerable<TSource> source;
-
-            private bool doMoveNext;
-            private IAsyncEnumerator<TSource> enumerator;
-
-            public SkipWhileAsyncIteratorWithTask(IAsyncEnumerable<TSource> source, Func<TSource, Task<bool>> predicate)
-            {
-                Debug.Assert(predicate != null);
-                Debug.Assert(source != null);
-
-                this.source = source;
-                this.predicate = predicate;
-            }
-
-            public override AsyncIterator<TSource> Clone()
-            {
-                return new SkipWhileAsyncIteratorWithTask<TSource>(source, predicate);
-            }
-
-            public override async Task DisposeAsync()
-            {
-                if (enumerator != null)
-                {
-                    await enumerator.DisposeAsync().ConfigureAwait(false);
-                    enumerator = null;
-                }
-
-                await base.DisposeAsync().ConfigureAwait(false);
-            }
-
-            protected override async Task<bool> MoveNextCore()
-            {
-                switch (state)
-                {
-                    case AsyncIteratorState.Allocated:
-                        enumerator = source.GetAsyncEnumerator();
-
-                        // skip elements as requested
-                        while (await enumerator.MoveNextAsync().ConfigureAwait(false))
-                        {
-                            var element = enumerator.Current;
-                            if (!await predicate(element).ConfigureAwait(false))
-                            {
-                                doMoveNext = false;
-                                state = AsyncIteratorState.Iterating;
-                                goto case AsyncIteratorState.Iterating;
-                            }
-                        }
-
-                        break;
-
-                    case AsyncIteratorState.Iterating:
-                        if (doMoveNext && await enumerator.MoveNextAsync().ConfigureAwait(false))
-                        {
-                            current = enumerator.Current;
-                            return true;
-                        }
-
-                        if (!doMoveNext)
-                        {
-                            current = enumerator.Current;
-                            doMoveNext = true;
-                            return true;
-                        }
-
-                        break;
-                }
-
-                await DisposeAsync().ConfigureAwait(false);
-                return false;
-            }
-        }
-
-        private sealed class SkipWhileWithIndexAsyncIteratorWithTask<TSource> : AsyncIterator<TSource>
-        {
-            private readonly Func<TSource, int, Task<bool>> predicate;
-            private readonly IAsyncEnumerable<TSource> source;
-
-            private bool doMoveNext;
-            private IAsyncEnumerator<TSource> enumerator;
-            private int index;
-
-            public SkipWhileWithIndexAsyncIteratorWithTask(IAsyncEnumerable<TSource> source, Func<TSource, int, Task<bool>> predicate)
-            {
-                Debug.Assert(predicate != null);
-                Debug.Assert(source != null);
-
-                this.source = source;
-                this.predicate = predicate;
-            }
-
-            public override AsyncIterator<TSource> Clone()
-            {
-                return new SkipWhileWithIndexAsyncIteratorWithTask<TSource>(source, predicate);
-            }
-
-            public override async Task DisposeAsync()
-            {
-                if (enumerator != null)
-                {
-                    await enumerator.DisposeAsync().ConfigureAwait(false);
-                    enumerator = null;
-                }
-
-                await base.DisposeAsync().ConfigureAwait(false);
-            }
-
-            protected override async Task<bool> MoveNextCore()
-            {
-                switch (state)
-                {
-                    case AsyncIteratorState.Allocated:
-                        enumerator = source.GetAsyncEnumerator();
-                        index = -1;
-
-                        // skip elements as requested
-                        while (await enumerator.MoveNextAsync().ConfigureAwait(false))
-                        {
-                            checked
-                            {
-                                index++;
-                            }
-
-                            var element = enumerator.Current;
-                            if (!await predicate(element, index).ConfigureAwait(false))
-                            {
-                                doMoveNext = false;
-                                state = AsyncIteratorState.Iterating;
-                                goto case AsyncIteratorState.Iterating;
-                            }
-                        }
-
-                        break;
-
-                    case AsyncIteratorState.Iterating:
-                        if (doMoveNext && await enumerator.MoveNextAsync().ConfigureAwait(false))
-                        {
-                            current = enumerator.Current;
-                            return true;
-                        }
-
-                        if (!doMoveNext)
-                        {
-                            current = enumerator.Current;
-                            doMoveNext = true;
-                            return true;
-                        }
-
-                        break;
-                }
-
-                await DisposeAsync().ConfigureAwait(false);
-                return false;
-            }
-        }
     }
 }

Ix.NET/Source/System.Interactive.Async/SkipLast.cs

@@ -0,0 +1,101 @@
+// 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.Diagnostics;
+using System.Threading.Tasks;
+
+namespace System.Linq
+{
+    public static partial class AsyncEnumerable
+    {
+        public static IAsyncEnumerable<TSource> SkipLast<TSource>(this IAsyncEnumerable<TSource> source, int count)
+        {
+            if (source == null)
+                throw new ArgumentNullException(nameof(source));
+
+            if (count <= 0)
+            {
+                // Return source if not actually skipping, but only if it's a type from here, to avoid
+                // issues if collections are used as keys or otherwise must not be aliased.
+                if (source is AsyncIterator<TSource>)
+                {
+                    return source;
+                }
+
+                count = 0;
+            }
+
+            return new SkipLastAsyncIterator<TSource>(source, count);
+        }
+
+        private sealed class SkipLastAsyncIterator<TSource> : AsyncIterator<TSource>
+        {
+            private readonly int count;
+            private readonly IAsyncEnumerable<TSource> source;
+
+            private IAsyncEnumerator<TSource> enumerator;
+            private Queue<TSource> queue;
+
+            public SkipLastAsyncIterator(IAsyncEnumerable<TSource> source, int count)
+            {
+                Debug.Assert(source != null);
+
+                this.source = source;
+                this.count = count;
+            }
+
+            public override AsyncIterator<TSource> Clone()
+            {
+                return new SkipLastAsyncIterator<TSource>(source, count);
+            }
+
+            public override async Task DisposeAsync()
+            {
+                if (enumerator != null)
+                {
+                    await enumerator.DisposeAsync().ConfigureAwait(false);
+                    enumerator = null;
+                }
+
+                queue = null; // release the memory
+
+                await base.DisposeAsync().ConfigureAwait(false);
+            }
+
+
+            protected override async Task<bool> MoveNextCore()
+            {
+                switch (state)
+                {
+                    case AsyncIteratorState.Allocated:
+                        enumerator = source.GetAsyncEnumerator();
+                        queue = new Queue<TSource>();
+
+                        state = AsyncIteratorState.Iterating;
+                        goto case AsyncIteratorState.Iterating;
+
+
+                    case AsyncIteratorState.Iterating:
+                        while (await enumerator.MoveNextAsync().ConfigureAwait(false))
+                        {
+                            var item = enumerator.Current;
+                            queue.Enqueue(item);
+
+                            if (queue.Count > count)
+                            {
+                                current = queue.Dequeue();
+                                return true;
+                            }
+                        }
+
+                        break;
+                }
+
+                await DisposeAsync().ConfigureAwait(false);
+                return false;
+            }
+        }
+    }
+}

Ix.NET/Source/System.Interactive.Async/SkipWhile.cs

@@ -0,0 +1,371 @@
+// 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.Diagnostics;
+using System.Threading.Tasks;
+
+namespace System.Linq
+{
+    public static partial class AsyncEnumerable
+    {
+        public static IAsyncEnumerable<TSource> SkipWhile<TSource>(this IAsyncEnumerable<TSource> source, Func<TSource, bool> predicate)
+        {
+            if (source == null)
+                throw new ArgumentNullException(nameof(source));
+            if (predicate == null)
+                throw new ArgumentNullException(nameof(predicate));
+
+            return new SkipWhileAsyncIterator<TSource>(source, predicate);
+        }
+
+        public static IAsyncEnumerable<TSource> SkipWhile<TSource>(this IAsyncEnumerable<TSource> source, Func<TSource, int, bool> predicate)
+        {
+            if (source == null)
+                throw new ArgumentNullException(nameof(source));
+            if (predicate == null)
+                throw new ArgumentNullException(nameof(predicate));
+
+            return new SkipWhileWithIndexAsyncIterator<TSource>(source, predicate);
+        }
+
+        public static IAsyncEnumerable<TSource> SkipWhile<TSource>(this IAsyncEnumerable<TSource> source, Func<TSource, Task<bool>> predicate)
+        {
+            if (source == null)
+                throw new ArgumentNullException(nameof(source));
+            if (predicate == null)
+                throw new ArgumentNullException(nameof(predicate));
+
+            return new SkipWhileAsyncIteratorWithTask<TSource>(source, predicate);
+        }
+
+        public static IAsyncEnumerable<TSource> SkipWhile<TSource>(this IAsyncEnumerable<TSource> source, Func<TSource, int, Task<bool>> predicate)
+        {
+            if (source == null)
+                throw new ArgumentNullException(nameof(source));
+            if (predicate == null)
+                throw new ArgumentNullException(nameof(predicate));
+
+            return new SkipWhileWithIndexAsyncIteratorWithTask<TSource>(source, predicate);
+        }
+
+        private sealed class SkipWhileAsyncIterator<TSource> : AsyncIterator<TSource>
+        {
+            private readonly Func<TSource, bool> predicate;
+            private readonly IAsyncEnumerable<TSource> source;
+
+            private bool doMoveNext;
+            private IAsyncEnumerator<TSource> enumerator;
+
+            public SkipWhileAsyncIterator(IAsyncEnumerable<TSource> source, Func<TSource, bool> predicate)
+            {
+                Debug.Assert(predicate != null);
+                Debug.Assert(source != null);
+
+                this.source = source;
+                this.predicate = predicate;
+            }
+
+            public override AsyncIterator<TSource> Clone()
+            {
+                return new SkipWhileAsyncIterator<TSource>(source, predicate);
+            }
+
+            public override async Task DisposeAsync()
+            {
+                if (enumerator != null)
+                {
+                    await enumerator.DisposeAsync().ConfigureAwait(false);
+                    enumerator = null;
+                }
+
+                await base.DisposeAsync().ConfigureAwait(false);
+            }
+
+            protected override async Task<bool> MoveNextCore()
+            {
+                switch (state)
+                {
+                    case AsyncIteratorState.Allocated:
+                        enumerator = source.GetAsyncEnumerator();
+
+                        // skip elements as requested
+                        while (await enumerator.MoveNextAsync().ConfigureAwait(false))
+                        {
+                            var element = enumerator.Current;
+                            if (!predicate(element))
+                            {
+                                doMoveNext = false;
+                                state = AsyncIteratorState.Iterating;
+                                goto case AsyncIteratorState.Iterating;
+                            }
+                        }
+
+                        break;
+
+                    case AsyncIteratorState.Iterating:
+                        if (doMoveNext && await enumerator.MoveNextAsync().ConfigureAwait(false))
+                        {
+                            current = enumerator.Current;
+                            return true;
+                        }
+
+                        if (!doMoveNext)
+                        {
+                            current = enumerator.Current;
+                            doMoveNext = true;
+                            return true;
+                        }
+
+                        break;
+                }
+
+                await DisposeAsync().ConfigureAwait(false);
+                return false;
+            }
+        }
+
+        private sealed class SkipWhileWithIndexAsyncIterator<TSource> : AsyncIterator<TSource>
+        {
+            private readonly Func<TSource, int, bool> predicate;
+            private readonly IAsyncEnumerable<TSource> source;
+
+            private bool doMoveNext;
+            private IAsyncEnumerator<TSource> enumerator;
+            private int index;
+
+            public SkipWhileWithIndexAsyncIterator(IAsyncEnumerable<TSource> source, Func<TSource, int, bool> predicate)
+            {
+                Debug.Assert(predicate != null);
+                Debug.Assert(source != null);
+
+                this.source = source;
+                this.predicate = predicate;
+            }
+
+            public override AsyncIterator<TSource> Clone()
+            {
+                return new SkipWhileWithIndexAsyncIterator<TSource>(source, predicate);
+            }
+
+            public override async Task DisposeAsync()
+            {
+                if (enumerator != null)
+                {
+                    await enumerator.DisposeAsync().ConfigureAwait(false);
+                    enumerator = null;
+                }
+
+                await base.DisposeAsync().ConfigureAwait(false);
+            }
+
+            protected override async Task<bool> MoveNextCore()
+            {
+                switch (state)
+                {
+                    case AsyncIteratorState.Allocated:
+                        enumerator = source.GetAsyncEnumerator();
+                        index = -1;
+
+                        // skip elements as requested
+                        while (await enumerator.MoveNextAsync().ConfigureAwait(false))
+                        {
+                            checked
+                            {
+                                index++;
+                            }
+
+                            var element = enumerator.Current;
+                            if (!predicate(element, index))
+                            {
+                                doMoveNext = false;
+                                state = AsyncIteratorState.Iterating;
+                                goto case AsyncIteratorState.Iterating;
+                            }
+                        }
+
+                        break;
+
+                    case AsyncIteratorState.Iterating:
+                        if (doMoveNext && await enumerator.MoveNextAsync().ConfigureAwait(false))
+                        {
+                            current = enumerator.Current;
+                            return true;
+                        }
+
+                        if (!doMoveNext)
+                        {
+                            current = enumerator.Current;
+                            doMoveNext = true;
+                            return true;
+                        }
+
+                        break;
+                }
+
+                await DisposeAsync().ConfigureAwait(false);
+                return false;
+            }
+        }
+
+        private sealed class SkipWhileAsyncIteratorWithTask<TSource> : AsyncIterator<TSource>
+        {
+            private readonly Func<TSource, Task<bool>> predicate;
+            private readonly IAsyncEnumerable<TSource> source;
+
+            private bool doMoveNext;
+            private IAsyncEnumerator<TSource> enumerator;
+
+            public SkipWhileAsyncIteratorWithTask(IAsyncEnumerable<TSource> source, Func<TSource, Task<bool>> predicate)
+            {
+                Debug.Assert(predicate != null);
+                Debug.Assert(source != null);
+
+                this.source = source;
+                this.predicate = predicate;
+            }
+
+            public override AsyncIterator<TSource> Clone()
+            {
+                return new SkipWhileAsyncIteratorWithTask<TSource>(source, predicate);
+            }
+
+            public override async Task DisposeAsync()
+            {
+                if (enumerator != null)
+                {
+                    await enumerator.DisposeAsync().ConfigureAwait(false);
+                    enumerator = null;
+                }
+
+                await base.DisposeAsync().ConfigureAwait(false);
+            }
+
+            protected override async Task<bool> MoveNextCore()
+            {
+                switch (state)
+                {
+                    case AsyncIteratorState.Allocated:
+                        enumerator = source.GetAsyncEnumerator();
+
+                        // skip elements as requested
+                        while (await enumerator.MoveNextAsync().ConfigureAwait(false))
+                        {
+                            var element = enumerator.Current;
+                            if (!await predicate(element).ConfigureAwait(false))
+                            {
+                                doMoveNext = false;
+                                state = AsyncIteratorState.Iterating;
+                                goto case AsyncIteratorState.Iterating;
+                            }
+                        }
+
+                        break;
+
+                    case AsyncIteratorState.Iterating:
+                        if (doMoveNext && await enumerator.MoveNextAsync().ConfigureAwait(false))
+                        {
+                            current = enumerator.Current;
+                            return true;
+                        }
+
+                        if (!doMoveNext)
+                        {
+                            current = enumerator.Current;
+                            doMoveNext = true;
+                            return true;
+                        }
+
+                        break;
+                }
+
+                await DisposeAsync().ConfigureAwait(false);
+                return false;
+            }
+        }
+
+        private sealed class SkipWhileWithIndexAsyncIteratorWithTask<TSource> : AsyncIterator<TSource>
+        {
+            private readonly Func<TSource, int, Task<bool>> predicate;
+            private readonly IAsyncEnumerable<TSource> source;
+
+            private bool doMoveNext;
+            private IAsyncEnumerator<TSource> enumerator;
+            private int index;
+
+            public SkipWhileWithIndexAsyncIteratorWithTask(IAsyncEnumerable<TSource> source, Func<TSource, int, Task<bool>> predicate)
+            {
+                Debug.Assert(predicate != null);
+                Debug.Assert(source != null);
+
+                this.source = source;
+                this.predicate = predicate;
+            }
+
+            public override AsyncIterator<TSource> Clone()
+            {
+                return new SkipWhileWithIndexAsyncIteratorWithTask<TSource>(source, predicate);
+            }
+
+            public override async Task DisposeAsync()
+            {
+                if (enumerator != null)
+                {
+                    await enumerator.DisposeAsync().ConfigureAwait(false);
+                    enumerator = null;
+                }
+
+                await base.DisposeAsync().ConfigureAwait(false);
+            }
+
+            protected override async Task<bool> MoveNextCore()
+            {
+                switch (state)
+                {
+                    case AsyncIteratorState.Allocated:
+                        enumerator = source.GetAsyncEnumerator();
+                        index = -1;
+
+                        // skip elements as requested
+                        while (await enumerator.MoveNextAsync().ConfigureAwait(false))
+                        {
+                            checked
+                            {
+                                index++;
+                            }
+
+                            var element = enumerator.Current;
+                            if (!await predicate(element, index).ConfigureAwait(false))
+                            {
+                                doMoveNext = false;
+                                state = AsyncIteratorState.Iterating;
+                                goto case AsyncIteratorState.Iterating;
+                            }
+                        }
+
+                        break;
+
+                    case AsyncIteratorState.Iterating:
+                        if (doMoveNext && await enumerator.MoveNextAsync().ConfigureAwait(false))
+                        {
+                            current = enumerator.Current;
+                            return true;
+                        }
+
+                        if (!doMoveNext)
+                        {
+                            current = enumerator.Current;
+                            doMoveNext = true;
+                            return true;
+                        }
+
+                        break;
+                }
+
+                await DisposeAsync().ConfigureAwait(false);
+                return false;
+            }
+        }
+    }
+}

Ix.NET/Source/System.Interactive.Async/Take.cs

@@ -23,59 +23,6 @@ namespace System.Linq
             return new TakeAsyncIterator<TSource>(source, count);
         }
 
-        public static IAsyncEnumerable<TSource> TakeLast<TSource>(this IAsyncEnumerable<TSource> source, int count)
-        {
-            if (source == null)
-                throw new ArgumentNullException(nameof(source));
-
-            if (count <= 0)
-            {
-                return Empty<TSource>();
-            }
-
-            return new TakeLastAsyncIterator<TSource>(source, count);
-        }
-
-        public static IAsyncEnumerable<TSource> TakeWhile<TSource>(this IAsyncEnumerable<TSource> source, Func<TSource, bool> predicate)
-        {
-            if (source == null)
-                throw new ArgumentNullException(nameof(source));
-            if (predicate == null)
-                throw new ArgumentNullException(nameof(predicate));
-
-            return new TakeWhileAsyncIterator<TSource>(source, predicate);
-        }
-
-        public static IAsyncEnumerable<TSource> TakeWhile<TSource>(this IAsyncEnumerable<TSource> source, Func<TSource, int, bool> predicate)
-        {
-            if (source == null)
-                throw new ArgumentNullException(nameof(source));
-            if (predicate == null)
-                throw new ArgumentNullException(nameof(predicate));
-
-            return new TakeWhileWithIndexAsyncIterator<TSource>(source, predicate);
-        }
-
-        public static IAsyncEnumerable<TSource> TakeWhile<TSource>(this IAsyncEnumerable<TSource> source, Func<TSource, Task<bool>> predicate)
-        {
-            if (source == null)
-                throw new ArgumentNullException(nameof(source));
-            if (predicate == null)
-                throw new ArgumentNullException(nameof(predicate));
-
-            return new TakeWhileAsyncIteratorWithTask<TSource>(source, predicate);
-        }
-
-        public static IAsyncEnumerable<TSource> TakeWhile<TSource>(this IAsyncEnumerable<TSource> source, Func<TSource, int, Task<bool>> predicate)
-        {
-            if (source == null)
-                throw new ArgumentNullException(nameof(source));
-            if (predicate == null)
-                throw new ArgumentNullException(nameof(predicate));
-
-            return new TakeWhileWithIndexAsyncIteratorWithTask<TSource>(source, predicate);
-        }
-
         private sealed class TakeAsyncIterator<TSource> : AsyncIterator<TSource>
         {
             private readonly int count;
@@ -135,366 +82,5 @@ namespace System.Linq
                 return false;
             }
         }
-
-        private sealed class TakeLastAsyncIterator<TSource> : AsyncIterator<TSource>
-        {
-            private readonly int count;
-            private readonly IAsyncEnumerable<TSource> source;
-
-            private IAsyncEnumerator<TSource> enumerator;
-            private bool isDone;
-            private Queue<TSource> queue;
-
-            public TakeLastAsyncIterator(IAsyncEnumerable<TSource> source, int count)
-            {
-                Debug.Assert(source != null);
-
-                this.source = source;
-                this.count = count;
-            }
-
-            public override AsyncIterator<TSource> Clone()
-            {
-                return new TakeLastAsyncIterator<TSource>(source, count);
-            }
-
-            public override async Task DisposeAsync()
-            {
-                if (enumerator != null)
-                {
-                    await enumerator.DisposeAsync().ConfigureAwait(false);
-                    enumerator = null;
-                }
-
-                queue = null; // release the memory
-
-                await base.DisposeAsync().ConfigureAwait(false);
-            }
-
-            protected override async Task<bool> MoveNextCore()
-            {
-                switch (state)
-                {
-                    case AsyncIteratorState.Allocated:
-                        enumerator = source.GetAsyncEnumerator();
-                        queue = new Queue<TSource>();
-                        isDone = false;
-
-                        state = AsyncIteratorState.Iterating;
-                        goto case AsyncIteratorState.Iterating;
-
-
-                    case AsyncIteratorState.Iterating:
-                        while (true)
-                        {
-                            if (!isDone)
-                            {
-                                if (await enumerator.MoveNextAsync().ConfigureAwait(false))
-                                {
-                                    if (count > 0)
-                                    {
-                                        var item = enumerator.Current;
-                                        if (queue.Count >= count)
-                                        {
-                                            queue.Dequeue();
-                                        }
-                                        queue.Enqueue(item);
-                                    }
-                                }
-                                else
-                                {
-                                    isDone = true;
-                                    // Dispose early here as we can
-                                    await enumerator.DisposeAsync().ConfigureAwait(false);
-                                    enumerator = null;
-                                }
-
-                                continue; // loop until queue is drained
-                            }
-
-                            if (queue.Count > 0)
-                            {
-                                current = queue.Dequeue();
-                                return true;
-                            }
-
-                            break; // while
-                        }
-
-                        break; // case
-                }
-
-                await DisposeAsync().ConfigureAwait(false);
-                return false;
-            }
-        }
-
-        private sealed class TakeWhileAsyncIterator<TSource> : AsyncIterator<TSource>
-        {
-            private readonly Func<TSource, bool> predicate;
-            private readonly IAsyncEnumerable<TSource> source;
-
-            private IAsyncEnumerator<TSource> enumerator;
-
-            public TakeWhileAsyncIterator(IAsyncEnumerable<TSource> source, Func<TSource, bool> predicate)
-            {
-                Debug.Assert(predicate != null);
-                Debug.Assert(source != null);
-
-                this.source = source;
-                this.predicate = predicate;
-            }
-
-            public override AsyncIterator<TSource> Clone()
-            {
-                return new TakeWhileAsyncIterator<TSource>(source, predicate);
-            }
-
-            public override async Task DisposeAsync()
-            {
-                if (enumerator != null)
-                {
-                    await enumerator.DisposeAsync().ConfigureAwait(false);
-                    enumerator = null;
-                }
-
-                await base.DisposeAsync().ConfigureAwait(false);
-            }
-
-            protected override async Task<bool> MoveNextCore()
-            {
-                switch (state)
-                {
-                    case AsyncIteratorState.Allocated:
-                        enumerator = source.GetAsyncEnumerator();
-
-                        state = AsyncIteratorState.Iterating;
-                        goto case AsyncIteratorState.Iterating;
-
-
-                    case AsyncIteratorState.Iterating:
-                        if (await enumerator.MoveNextAsync().ConfigureAwait(false))
-                        {
-                            var item = enumerator.Current;
-                            if (!predicate(item))
-                            {
-                                break;
-                            }
-
-                            current = item;
-                            return true;
-                        }
-
-                        break;
-                }
-
-                await DisposeAsync().ConfigureAwait(false);
-                return false;
-            }
-        }
-
-        private sealed class TakeWhileWithIndexAsyncIterator<TSource> : AsyncIterator<TSource>
-        {
-            private readonly Func<TSource, int, bool> predicate;
-            private readonly IAsyncEnumerable<TSource> source;
-
-            private IAsyncEnumerator<TSource> enumerator;
-            private int index;
-
-            public TakeWhileWithIndexAsyncIterator(IAsyncEnumerable<TSource> source, Func<TSource, int, bool> predicate)
-            {
-                Debug.Assert(predicate != null);
-                Debug.Assert(source != null);
-
-                this.source = source;
-                this.predicate = predicate;
-            }
-
-            public override AsyncIterator<TSource> Clone()
-            {
-                return new TakeWhileWithIndexAsyncIterator<TSource>(source, predicate);
-            }
-
-            public override async Task DisposeAsync()
-            {
-                if (enumerator != null)
-                {
-                    await enumerator.DisposeAsync().ConfigureAwait(false);
-                    enumerator = null;
-                }
-
-                await base.DisposeAsync().ConfigureAwait(false);
-            }
-
-            protected override async Task<bool> MoveNextCore()
-            {
-                switch (state)
-                {
-                    case AsyncIteratorState.Allocated:
-                        enumerator = source.GetAsyncEnumerator();
-                        index = -1;
-                        state = AsyncIteratorState.Iterating;
-                        goto case AsyncIteratorState.Iterating;
-
-
-                    case AsyncIteratorState.Iterating:
-                        if (await enumerator.MoveNextAsync().ConfigureAwait(false))
-                        {
-                            var item = enumerator.Current;
-                            checked
-                            {
-                                index++;
-                            }
-
-                            if (!predicate(item, index))
-                            {
-                                break;
-                            }
-
-                            current = item;
-                            return true;
-                        }
-
-                        break;
-                }
-
-                await DisposeAsync().ConfigureAwait(false);
-                return false;
-            }
-        }
-
-        private sealed class TakeWhileAsyncIteratorWithTask<TSource> : AsyncIterator<TSource>
-        {
-            private readonly Func<TSource, Task<bool>> predicate;
-            private readonly IAsyncEnumerable<TSource> source;
-
-            private IAsyncEnumerator<TSource> enumerator;
-
-            public TakeWhileAsyncIteratorWithTask(IAsyncEnumerable<TSource> source, Func<TSource, Task<bool>> predicate)
-            {
-                Debug.Assert(predicate != null);
-                Debug.Assert(source != null);
-
-                this.source = source;
-                this.predicate = predicate;
-            }
-
-            public override AsyncIterator<TSource> Clone()
-            {
-                return new TakeWhileAsyncIteratorWithTask<TSource>(source, predicate);
-            }
-
-            public override async Task DisposeAsync()
-            {
-                if (enumerator != null)
-                {
-                    await enumerator.DisposeAsync().ConfigureAwait(false);
-                    enumerator = null;
-                }
-
-                await base.DisposeAsync().ConfigureAwait(false);
-            }
-
-            protected override async Task<bool> MoveNextCore()
-            {
-                switch (state)
-                {
-                    case AsyncIteratorState.Allocated:
-                        enumerator = source.GetAsyncEnumerator();
-
-                        state = AsyncIteratorState.Iterating;
-                        goto case AsyncIteratorState.Iterating;
-
-
-                    case AsyncIteratorState.Iterating:
-                        if (await enumerator.MoveNextAsync().ConfigureAwait(false))
-                        {
-                            var item = enumerator.Current;
-                            if (!await predicate(item).ConfigureAwait(false))
-                            {
-                                break;
-                            }
-
-                            current = item;
-                            return true;
-                        }
-
-                        break;
-                }
-
-                await DisposeAsync().ConfigureAwait(false);
-                return false;
-            }
-        }
-
-        private sealed class TakeWhileWithIndexAsyncIteratorWithTask<TSource> : AsyncIterator<TSource>
-        {
-            private readonly Func<TSource, int, Task<bool>> predicate;
-            private readonly IAsyncEnumerable<TSource> source;
-
-            private IAsyncEnumerator<TSource> enumerator;
-            private int index;
-
-            public TakeWhileWithIndexAsyncIteratorWithTask(IAsyncEnumerable<TSource> source, Func<TSource, int, Task<bool>> predicate)
-            {
-                Debug.Assert(predicate != null);
-                Debug.Assert(source != null);
-
-                this.source = source;
-                this.predicate = predicate;
-            }
-
-            public override AsyncIterator<TSource> Clone()
-            {
-                return new TakeWhileWithIndexAsyncIteratorWithTask<TSource>(source, predicate);
-            }
-
-            public override async Task DisposeAsync()
-            {
-                if (enumerator != null)
-                {
-                    await enumerator.DisposeAsync().ConfigureAwait(false);
-                    enumerator = null;
-                }
-
-                await base.DisposeAsync().ConfigureAwait(false);
-            }
-
-            protected override async Task<bool> MoveNextCore()
-            {
-                switch (state)
-                {
-                    case AsyncIteratorState.Allocated:
-                        enumerator = source.GetAsyncEnumerator();
-                        index = -1;
-                        state = AsyncIteratorState.Iterating;
-                        goto case AsyncIteratorState.Iterating;
-
-
-                    case AsyncIteratorState.Iterating:
-                        if (await enumerator.MoveNextAsync().ConfigureAwait(false))
-                        {
-                            var item = enumerator.Current;
-                            checked
-                            {
-                                index++;
-                            }
-
-                            if (!await predicate(item, index).ConfigureAwait(false))
-                            {
-                                break;
-                            }
-
-                            current = item;
-                            return true;
-                        }
-
-                        break;
-                }
-
-                await DisposeAsync().ConfigureAwait(false);
-                return false;
-            }
-        }
     }
 }

Ix.NET/Source/System.Interactive.Async/TakeLast.cs

@@ -0,0 +1,119 @@
+// 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.Diagnostics;
+using System.Threading.Tasks;
+
+namespace System.Linq
+{
+    public static partial class AsyncEnumerable
+    {
+        public static IAsyncEnumerable<TSource> TakeLast<TSource>(this IAsyncEnumerable<TSource> source, int count)
+        {
+            if (source == null)
+                throw new ArgumentNullException(nameof(source));
+
+            if (count <= 0)
+            {
+                return Empty<TSource>();
+            }
+
+            return new TakeLastAsyncIterator<TSource>(source, count);
+        }
+
+        private sealed class TakeLastAsyncIterator<TSource> : AsyncIterator<TSource>
+        {
+            private readonly int count;
+            private readonly IAsyncEnumerable<TSource> source;
+
+            private IAsyncEnumerator<TSource> enumerator;
+            private bool isDone;
+            private Queue<TSource> queue;
+
+            public TakeLastAsyncIterator(IAsyncEnumerable<TSource> source, int count)
+            {
+                Debug.Assert(source != null);
+
+                this.source = source;
+                this.count = count;
+            }
+
+            public override AsyncIterator<TSource> Clone()
+            {
+                return new TakeLastAsyncIterator<TSource>(source, count);
+            }
+
+            public override async Task DisposeAsync()
+            {
+                if (enumerator != null)
+                {
+                    await enumerator.DisposeAsync().ConfigureAwait(false);
+                    enumerator = null;
+                }
+
+                queue = null; // release the memory
+
+                await base.DisposeAsync().ConfigureAwait(false);
+            }
+
+            protected override async Task<bool> MoveNextCore()
+            {
+                switch (state)
+                {
+                    case AsyncIteratorState.Allocated:
+                        enumerator = source.GetAsyncEnumerator();
+                        queue = new Queue<TSource>();
+                        isDone = false;
+
+                        state = AsyncIteratorState.Iterating;
+                        goto case AsyncIteratorState.Iterating;
+
+
+                    case AsyncIteratorState.Iterating:
+                        while (true)
+                        {
+                            if (!isDone)
+                            {
+                                if (await enumerator.MoveNextAsync().ConfigureAwait(false))
+                                {
+                                    if (count > 0)
+                                    {
+                                        var item = enumerator.Current;
+                                        if (queue.Count >= count)
+                                        {
+                                            queue.Dequeue();
+                                        }
+                                        queue.Enqueue(item);
+                                    }
+                                }
+                                else
+                                {
+                                    isDone = true;
+                                    // Dispose early here as we can
+                                    await enumerator.DisposeAsync().ConfigureAwait(false);
+                                    enumerator = null;
+                                }
+
+                                continue; // loop until queue is drained
+                            }
+
+                            if (queue.Count > 0)
+                            {
+                                current = queue.Dequeue();
+                                return true;
+                            }
+
+                            break; // while
+                        }
+
+                        break; // case
+                }
+
+                await DisposeAsync().ConfigureAwait(false);
+                return false;
+            }
+        }
+    }
+}

Ix.NET/Source/System.Interactive.Async/TakeWhile.cs

@@ -0,0 +1,321 @@
+// 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.Diagnostics;
+using System.Threading.Tasks;
+
+namespace System.Linq
+{
+    public static partial class AsyncEnumerable
+    {
+        public static IAsyncEnumerable<TSource> TakeWhile<TSource>(this IAsyncEnumerable<TSource> source, Func<TSource, bool> predicate)
+        {
+            if (source == null)
+                throw new ArgumentNullException(nameof(source));
+            if (predicate == null)
+                throw new ArgumentNullException(nameof(predicate));
+
+            return new TakeWhileAsyncIterator<TSource>(source, predicate);
+        }
+
+        public static IAsyncEnumerable<TSource> TakeWhile<TSource>(this IAsyncEnumerable<TSource> source, Func<TSource, int, bool> predicate)
+        {
+            if (source == null)
+                throw new ArgumentNullException(nameof(source));
+            if (predicate == null)
+                throw new ArgumentNullException(nameof(predicate));
+
+            return new TakeWhileWithIndexAsyncIterator<TSource>(source, predicate);
+        }
+
+        public static IAsyncEnumerable<TSource> TakeWhile<TSource>(this IAsyncEnumerable<TSource> source, Func<TSource, Task<bool>> predicate)
+        {
+            if (source == null)
+                throw new ArgumentNullException(nameof(source));
+            if (predicate == null)
+                throw new ArgumentNullException(nameof(predicate));
+
+            return new TakeWhileAsyncIteratorWithTask<TSource>(source, predicate);
+        }
+
+        public static IAsyncEnumerable<TSource> TakeWhile<TSource>(this IAsyncEnumerable<TSource> source, Func<TSource, int, Task<bool>> predicate)
+        {
+            if (source == null)
+                throw new ArgumentNullException(nameof(source));
+            if (predicate == null)
+                throw new ArgumentNullException(nameof(predicate));
+
+            return new TakeWhileWithIndexAsyncIteratorWithTask<TSource>(source, predicate);
+        }
+
+        private sealed class TakeWhileAsyncIterator<TSource> : AsyncIterator<TSource>
+        {
+            private readonly Func<TSource, bool> predicate;
+            private readonly IAsyncEnumerable<TSource> source;
+
+            private IAsyncEnumerator<TSource> enumerator;
+
+            public TakeWhileAsyncIterator(IAsyncEnumerable<TSource> source, Func<TSource, bool> predicate)
+            {
+                Debug.Assert(predicate != null);
+                Debug.Assert(source != null);
+
+                this.source = source;
+                this.predicate = predicate;
+            }
+
+            public override AsyncIterator<TSource> Clone()
+            {
+                return new TakeWhileAsyncIterator<TSource>(source, predicate);
+            }
+
+            public override async Task DisposeAsync()
+            {
+                if (enumerator != null)
+                {
+                    await enumerator.DisposeAsync().ConfigureAwait(false);
+                    enumerator = null;
+                }
+
+                await base.DisposeAsync().ConfigureAwait(false);
+            }
+
+            protected override async Task<bool> MoveNextCore()
+            {
+                switch (state)
+                {
+                    case AsyncIteratorState.Allocated:
+                        enumerator = source.GetAsyncEnumerator();
+
+                        state = AsyncIteratorState.Iterating;
+                        goto case AsyncIteratorState.Iterating;
+
+
+                    case AsyncIteratorState.Iterating:
+                        if (await enumerator.MoveNextAsync().ConfigureAwait(false))
+                        {
+                            var item = enumerator.Current;
+                            if (!predicate(item))
+                            {
+                                break;
+                            }
+
+                            current = item;
+                            return true;
+                        }
+
+                        break;
+                }
+
+                await DisposeAsync().ConfigureAwait(false);
+                return false;
+            }
+        }
+
+        private sealed class TakeWhileWithIndexAsyncIterator<TSource> : AsyncIterator<TSource>
+        {
+            private readonly Func<TSource, int, bool> predicate;
+            private readonly IAsyncEnumerable<TSource> source;
+
+            private IAsyncEnumerator<TSource> enumerator;
+            private int index;
+
+            public TakeWhileWithIndexAsyncIterator(IAsyncEnumerable<TSource> source, Func<TSource, int, bool> predicate)
+            {
+                Debug.Assert(predicate != null);
+                Debug.Assert(source != null);
+
+                this.source = source;
+                this.predicate = predicate;
+            }
+
+            public override AsyncIterator<TSource> Clone()
+            {
+                return new TakeWhileWithIndexAsyncIterator<TSource>(source, predicate);
+            }
+
+            public override async Task DisposeAsync()
+            {
+                if (enumerator != null)
+                {
+                    await enumerator.DisposeAsync().ConfigureAwait(false);
+                    enumerator = null;
+                }
+
+                await base.DisposeAsync().ConfigureAwait(false);
+            }
+
+            protected override async Task<bool> MoveNextCore()
+            {
+                switch (state)
+                {
+                    case AsyncIteratorState.Allocated:
+                        enumerator = source.GetAsyncEnumerator();
+                        index = -1;
+                        state = AsyncIteratorState.Iterating;
+                        goto case AsyncIteratorState.Iterating;
+
+
+                    case AsyncIteratorState.Iterating:
+                        if (await enumerator.MoveNextAsync().ConfigureAwait(false))
+                        {
+                            var item = enumerator.Current;
+                            checked
+                            {
+                                index++;
+                            }
+
+                            if (!predicate(item, index))
+                            {
+                                break;
+                            }
+
+                            current = item;
+                            return true;
+                        }
+
+                        break;
+                }
+
+                await DisposeAsync().ConfigureAwait(false);
+                return false;
+            }
+        }
+
+        private sealed class TakeWhileAsyncIteratorWithTask<TSource> : AsyncIterator<TSource>
+        {
+            private readonly Func<TSource, Task<bool>> predicate;
+            private readonly IAsyncEnumerable<TSource> source;
+
+            private IAsyncEnumerator<TSource> enumerator;
+
+            public TakeWhileAsyncIteratorWithTask(IAsyncEnumerable<TSource> source, Func<TSource, Task<bool>> predicate)
+            {
+                Debug.Assert(predicate != null);
+                Debug.Assert(source != null);
+
+                this.source = source;
+                this.predicate = predicate;
+            }
+
+            public override AsyncIterator<TSource> Clone()
+            {
+                return new TakeWhileAsyncIteratorWithTask<TSource>(source, predicate);
+            }
+
+            public override async Task DisposeAsync()
+            {
+                if (enumerator != null)
+                {
+                    await enumerator.DisposeAsync().ConfigureAwait(false);
+                    enumerator = null;
+                }
+
+                await base.DisposeAsync().ConfigureAwait(false);
+            }
+
+            protected override async Task<bool> MoveNextCore()
+            {
+                switch (state)
+                {
+                    case AsyncIteratorState.Allocated:
+                        enumerator = source.GetAsyncEnumerator();
+
+                        state = AsyncIteratorState.Iterating;
+                        goto case AsyncIteratorState.Iterating;
+
+
+                    case AsyncIteratorState.Iterating:
+                        if (await enumerator.MoveNextAsync().ConfigureAwait(false))
+                        {
+                            var item = enumerator.Current;
+                            if (!await predicate(item).ConfigureAwait(false))
+                            {
+                                break;
+                            }
+
+                            current = item;
+                            return true;
+                        }
+
+                        break;
+                }
+
+                await DisposeAsync().ConfigureAwait(false);
+                return false;
+            }
+        }
+
+        private sealed class TakeWhileWithIndexAsyncIteratorWithTask<TSource> : AsyncIterator<TSource>
+        {
+            private readonly Func<TSource, int, Task<bool>> predicate;
+            private readonly IAsyncEnumerable<TSource> source;
+
+            private IAsyncEnumerator<TSource> enumerator;
+            private int index;
+
+            public TakeWhileWithIndexAsyncIteratorWithTask(IAsyncEnumerable<TSource> source, Func<TSource, int, Task<bool>> predicate)
+            {
+                Debug.Assert(predicate != null);
+                Debug.Assert(source != null);
+
+                this.source = source;
+                this.predicate = predicate;
+            }
+
+            public override AsyncIterator<TSource> Clone()
+            {
+                return new TakeWhileWithIndexAsyncIteratorWithTask<TSource>(source, predicate);
+            }
+
+            public override async Task DisposeAsync()
+            {
+                if (enumerator != null)
+                {
+                    await enumerator.DisposeAsync().ConfigureAwait(false);
+                    enumerator = null;
+                }
+
+                await base.DisposeAsync().ConfigureAwait(false);
+            }
+
+            protected override async Task<bool> MoveNextCore()
+            {
+                switch (state)
+                {
+                    case AsyncIteratorState.Allocated:
+                        enumerator = source.GetAsyncEnumerator();
+                        index = -1;
+                        state = AsyncIteratorState.Iterating;
+                        goto case AsyncIteratorState.Iterating;
+
+
+                    case AsyncIteratorState.Iterating:
+                        if (await enumerator.MoveNextAsync().ConfigureAwait(false))
+                        {
+                            var item = enumerator.Current;
+                            checked
+                            {
+                                index++;
+                            }
+
+                            if (!await predicate(item, index).ConfigureAwait(false))
+                            {
+                                break;
+                            }
+
+                            current = item;
+                            return true;
+                        }
+
+                        break;
+                }
+
+                await DisposeAsync().ConfigureAwait(false);
+                return false;
+            }
+        }
+    }
+}