From b2a00bf33df717da8041f824a1dcbc160b1501f4 Mon Sep 17 00:00:00 2001
From: Claude <noreply@anthropic.com>
Date: Sat, 26 Sep 2026 05:27:27 +0000
Subject: [PATCH] fix: read ReplaceWith's new items before clearing the
 collection [patch]

ReplaceWith cleared the collection and then enumerated newItems, so a
lazy query over the collection (items.Where(...)) or the collection
itself yielded nothing and the collection ended up empty. Snapshot
newItems into an array before clearing.

Fixes ktsu-dev/Extensions#132

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012Hhb8knddbu4LRSs2uu9jR
---
 Extensions.Test/CollectionExtensionsTests.cs | 20 ++++++++++++++++++++
 Extensions/CollectionExtensions.cs           |  4 +++-
 2 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/Extensions.Test/CollectionExtensionsTests.cs b/Extensions.Test/CollectionExtensionsTests.cs
index 9fff389..38e3ba0 100644
--- a/Extensions.Test/CollectionExtensionsTests.cs
+++ b/Extensions.Test/CollectionExtensionsTests.cs
@@ -239,4 +239,24 @@ public void ReplaceWithNewItemsContainingNullsReplacesCorrectly()
 
 		CollectionAssert.AreEqual(new List<string?> { "x", null, "z" }, collection);
 	}
+
+	[TestMethod]
+	public void ReplaceWithLazyQueryOverSameCollectionKeepsMatchingItems()
+	{
+		List<int> collection = [1, 2, 3, 4];
+
+		collection.ReplaceWith(collection.Where(x => x > 2));
+
+		CollectionAssert.AreEqual(new List<int> { 3, 4 }, collection);
+	}
+
+	[TestMethod]
+	public void ReplaceWithSameCollectionKeepsItems()
+	{
+		List<int> collection = [1, 2, 3];
+
+		collection.ReplaceWith(collection);
+
+		CollectionAssert.AreEqual(new List<int> { 1, 2, 3 }, collection);
+	}
 }
diff --git a/Extensions/CollectionExtensions.cs b/Extensions/CollectionExtensions.cs
index 4d65af0..295812d 100644
--- a/Extensions/CollectionExtensions.cs
+++ b/Extensions/CollectionExtensions.cs
@@ -62,7 +62,9 @@ public static void ReplaceWith<T>(this ICollection<T> oldItems, IEnumerable<T> n
 		}
 #pragma warning restore KTSU0004 // Use Ensure.NotNull instead of manual null check
 
+		// Materialize first: newItems may be the collection itself or a lazy query over it, which Clear would empty
+		T[] snapshot = [.. newItems];
 		oldItems.Clear();
-		oldItems.AddFrom(newItems);
+		oldItems.AddFrom(snapshot);
 	}
 }