Splitting ElementAt and ElementAtOrDefault.

Ix.NET/Source/System.Linq.Async/System/Linq/Operators/ElementAt.cs

@@ -28,24 +28,6 @@ namespace System.Linq
             return ElementAt_(source, index, cancellationToken);
         }
 
-        public static Task<TSource> ElementAtOrDefault<TSource>(this IAsyncEnumerable<TSource> source, int index)
-        {
-            if (source == null)
-                throw new ArgumentNullException(nameof(source));
-
-            return ElementAtOrDefault(source, index, CancellationToken.None);
-        }
-
-        public static Task<TSource> ElementAtOrDefault<TSource>(this IAsyncEnumerable<TSource> source, int index, CancellationToken cancellationToken)
-        {
-            if (source == null)
-                throw new ArgumentNullException(nameof(source));
-            if (index < 0)
-                throw new ArgumentOutOfRangeException(nameof(index));
-
-            return ElementAtOrDefault_(source, index, cancellationToken);
-        }
-
         private static async Task<TSource> ElementAt_<TSource>(IAsyncEnumerable<TSource> source, int index, CancellationToken cancellationToken)
         {
             if (source is IList<TSource> list)
@@ -77,32 +59,5 @@ namespace System.Linq
 
             throw new ArgumentOutOfRangeException(nameof(index));
         }
-
-        private static async Task<TSource> ElementAtOrDefault_<TSource>(IAsyncEnumerable<TSource> source, int index, CancellationToken cancellationToken)
-        {
-            if (index >= 0)
-            {
-                var e = source.GetAsyncEnumerator();
-
-                try
-                {
-                    while (await e.MoveNextAsync(cancellationToken).ConfigureAwait(false))
-                    {
-                        if (index == 0)
-                        {
-                            return e.Current;
-                        }
-
-                        index--;
-                    }
-                }
-                finally
-                {
-                    await e.DisposeAsync().ConfigureAwait(false);
-                }
-            }
-
-            return default(TSource);
-        }
     }
 }

Ix.NET/Source/System.Linq.Async/System/Linq/Operators/ElementAtOrDefault.cs

@@ -0,0 +1,58 @@
+// 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.Threading;
+using System.Threading.Tasks;
+
+namespace System.Linq
+{
+    public static partial class AsyncEnumerable
+    {
+        public static Task<TSource> ElementAtOrDefault<TSource>(this IAsyncEnumerable<TSource> source, int index)
+        {
+            if (source == null)
+                throw new ArgumentNullException(nameof(source));
+
+            return ElementAtOrDefault(source, index, CancellationToken.None);
+        }
+
+        public static Task<TSource> ElementAtOrDefault<TSource>(this IAsyncEnumerable<TSource> source, int index, CancellationToken cancellationToken)
+        {
+            if (source == null)
+                throw new ArgumentNullException(nameof(source));
+            if (index < 0)
+                throw new ArgumentOutOfRangeException(nameof(index));
+
+            return ElementAtOrDefault_(source, index, cancellationToken);
+        }
+
+        private static async Task<TSource> ElementAtOrDefault_<TSource>(IAsyncEnumerable<TSource> source, int index, CancellationToken cancellationToken)
+        {
+            if (index >= 0)
+            {
+                var e = source.GetAsyncEnumerator();
+
+                try
+                {
+                    while (await e.MoveNextAsync(cancellationToken).ConfigureAwait(false))
+                    {
+                        if (index == 0)
+                        {
+                            return e.Current;
+                        }
+
+                        index--;
+                    }
+                }
+                finally
+                {
+                    await e.DisposeAsync().ConfigureAwait(false);
+                }
+            }
+
+            return default(TSource);
+        }
+    }
+}