From a63d56b0b4764859eae0246ebfdfb2b089a381f3 Mon Sep 17 00:00:00 2001
From: sakno <roman.sakno@gmail.com>
Date: Sat, 13 Jul 2024 20:19:48 +0300
Subject: [PATCH] Corner case with empty set of tasks

---
 .../Tasks/TaskCompletionPipe.Consumer.cs      | 40 +++++++++++++++----
 1 file changed, 32 insertions(+), 8 deletions(-)

diff --git a/src/DotNext.Threading/Threading/Tasks/TaskCompletionPipe.Consumer.cs b/src/DotNext.Threading/Threading/Tasks/TaskCompletionPipe.Consumer.cs
index 8c1ed11f4..95e1c3475 100644
--- a/src/DotNext.Threading/Threading/Tasks/TaskCompletionPipe.Consumer.cs
+++ b/src/DotNext.Threading/Threading/Tasks/TaskCompletionPipe.Consumer.cs
@@ -1,8 +1,11 @@
 using System.Runtime.InteropServices;
+using DotNext.Collections.Generic;
 using Debug = System.Diagnostics.Debug;
 
 namespace DotNext.Threading.Tasks;
 
+using static Collections.Generic.AsyncEnumerable;
+
 /// <summary>
 /// Provides various extension methods for <see cref="TaskCompletionPipe{T}"/> class.
 /// </summary>
@@ -16,7 +19,7 @@ public static class TaskCompletionPipe
     /// <returns>The asynchronous consuming collection.</returns>
     public static Consumer<T> GetConsumer<T>(this TaskCompletionPipe<Task<T>> pipe)
         => new(pipe);
-    
+
     /// <summary>
     /// Gets a collection over tasks to be available as they complete.
     /// </summary>
@@ -25,9 +28,19 @@ public static Consumer<T> GetConsumer<T>(this TaskCompletionPipe<Task<T>> pipe)
     /// <returns>A collection over task results to be available as they complete.</returns>
     public static Consumer<T> GetConsumer<T>(this ReadOnlySpan<Task<T>> tasks)
     {
-        var pipe = new TaskCompletionPipe<Task<T>>();
-        pipe.Add(tasks, complete: true);
-        return new(pipe);
+        Consumer<T> result;
+        if (tasks.IsEmpty)
+        {
+            result = default;
+        }
+        else
+        {
+            var pipe = new TaskCompletionPipe<Task<T>>();
+            pipe.Add(tasks, complete: true);
+            result = new(pipe);
+        }
+
+        return result;
     }
 
     /// <summary>
@@ -39,9 +52,20 @@ public static Consumer<T> GetConsumer<T>(this ReadOnlySpan<Task<T>> tasks)
     public static IAsyncEnumerable<T> Create<T>(ReadOnlySpan<T> tasks)
         where T : Task
     {
-        var pipe = new TaskCompletionPipe<T>();
-        pipe.Add(tasks, complete: true);
-        return pipe;
+        IAsyncEnumerable<T> result;
+
+        if (tasks.IsEmpty)
+        {
+            result = Empty<T>();
+        }
+        else
+        {
+            var pipe = new TaskCompletionPipe<T>();
+            pipe.Add(tasks, complete: true);
+            result = pipe;
+        }
+
+        return result;
     }
 
     private static async IAsyncEnumerator<T> GetAsyncEnumerator<T>(TaskCompletionPipe<Task<T>> pipe, uint expectedVersion, CancellationToken token)
@@ -75,6 +99,6 @@ internal Consumer(TaskCompletionPipe<Task<T>> pipe)
         /// <param name="token">The token that can be used to cancel the operation.</param>
         /// <returns>The asynchronous enumerator over completed tasks.</returns>
         public IAsyncEnumerator<T> GetAsyncEnumerator(CancellationToken token = default)
-            => GetAsyncEnumerator<T>(pipe, pipe.Version, token);
+            => pipe is null ? Empty<T>().GetAsyncEnumerator(token) : GetAsyncEnumerator<T>(pipe, pipe.Version, token);
     }
 }
\ No newline at end of file