From aeb6598d28682eaf0b2c802232d633b7c05bf1ba Mon Sep 17 00:00:00 2001
From: sakno <roman.sakno@gmail.com>
Date: Tue, 8 Oct 2024 18:24:01 +0300
Subject: [PATCH] Added async singleton collection

---
 .../Collections/Generic/AsyncEnumerableTests.cs          | 7 +++++++
 src/DotNext/Collections/Generic/AsyncEnumerable.cs       | 9 +++++++++
 src/DotNext/Collections/Specialized/SingletonList.cs     | 6 +++++-
 3 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/src/DotNext.Tests/Collections/Generic/AsyncEnumerableTests.cs b/src/DotNext.Tests/Collections/Generic/AsyncEnumerableTests.cs
index 2ebb718aa..6ed4ad29f 100644
--- a/src/DotNext.Tests/Collections/Generic/AsyncEnumerableTests.cs
+++ b/src/DotNext.Tests/Collections/Generic/AsyncEnumerableTests.cs
@@ -97,4 +97,11 @@ public static async Task SkipNullsTestAsync()
         True(Array.Exists(array, "a".Equals));
         True(Array.Exists(array, "b".Equals));
     }
+
+    [Fact]
+    public static void Singleton()
+    {
+        var enumerable = AsyncEnumerable.Singleton(42);
+        Equal(42, Single(enumerable));
+    }
 }
\ No newline at end of file
diff --git a/src/DotNext/Collections/Generic/AsyncEnumerable.cs b/src/DotNext/Collections/Generic/AsyncEnumerable.cs
index 5eb5bcdf2..50fead5c8 100644
--- a/src/DotNext/Collections/Generic/AsyncEnumerable.cs
+++ b/src/DotNext/Collections/Generic/AsyncEnumerable.cs
@@ -219,4 +219,13 @@ public static IAsyncEnumerable<T> Throw<T>(Exception e)
 
         return new ThrowingEnumerator<T>(e);
     }
+
+    /// <summary>
+    /// Constructs read-only sequence with a single item in it.
+    /// </summary>
+    /// <param name="item">An item to be placed into list.</param>
+    /// <typeparam name="T">Type of list items.</typeparam>
+    /// <returns>Read-only list containing single item.</returns>
+    public static IAsyncEnumerable<T> Singleton<T>(T item)
+        => new Specialized.SingletonList<T> { Item = item };
 }
\ No newline at end of file
diff --git a/src/DotNext/Collections/Specialized/SingletonList.cs b/src/DotNext/Collections/Specialized/SingletonList.cs
index 53b9613fa..4e98514b6 100644
--- a/src/DotNext/Collections/Specialized/SingletonList.cs
+++ b/src/DotNext/Collections/Specialized/SingletonList.cs
@@ -12,7 +12,7 @@ namespace DotNext.Collections.Specialized;
 /// </summary>
 /// <typeparam name="T">The type of the element in the list.</typeparam>
 [StructLayout(LayoutKind.Auto)]
-public struct SingletonList<T> : IReadOnlyList<T>, IList<T>, ITuple, IReadOnlySet<T>
+public struct SingletonList<T> : IReadOnlyList<T>, IList<T>, ITuple, IReadOnlySet<T>, IAsyncEnumerable<T>
 {
     /// <summary>
     /// Represents an enumerator over the collection containing a single element.
@@ -145,6 +145,10 @@ readonly IEnumerator<T> IEnumerable<T>.GetEnumerator()
     readonly IEnumerator IEnumerable.GetEnumerator()
         => GetEnumerator().ToClassicEnumerator<Enumerator, T>();
 
+    /// <inheritdoc />
+    readonly IAsyncEnumerator<T> IAsyncEnumerable<T>.GetAsyncEnumerator(CancellationToken token)
+        => GetEnumerator().ToAsyncEnumerator<Enumerator, T>(token);
+
     /// <summary>
     /// Converts a value to the read-only list.
     /// </summary>