Remove set items from storage using the set's comparer

Containers.Test/ContiguousSetTests.cs

@@ -452,4 +452,37 @@ public void WorksWithStrings()
 		Assert.Contains("alpha", set);
 		Assert.Contains("bravo", set);
 	}
+
+	[TestMethod]
+	public void Remove_WithCustomComparer_RemovesItemEqualOnlyUnderComparer()
+	{
+		// Arrange
+		ContiguousSet<string> set = new(StringComparer.OrdinalIgnoreCase) { "Apple", "Banana" };
+
+		// Act
+		bool removed = set.Remove("APPLE");
+
+		// Assert
+		Assert.IsTrue(removed);
+		Assert.HasCount(1, set);
+		Assert.IsFalse(set.Contains("apple"));
+		string[] expectedItems = ["Banana"];
+		Assert.AreSequenceEqual(expectedItems, set);
+	}
+
+	[TestMethod]
+	public void Remove_WithCustomComparer_ThenAdd_KeepsSingleElement()
+	{
+		// Arrange
+		ContiguousSet<string> set = new(StringComparer.OrdinalIgnoreCase) { "Apple" };
+
+		// Act
+		set.Remove("APPLE");
+		set.Add("apple");
+
+		// Assert
+		Assert.HasCount(1, set);
+		string[] expectedItems = ["apple"];
+		Assert.AreSequenceEqual(expectedItems, set);
+	}
 }

Containers.Test/InsertionOrderSetTests.cs

@@ -322,4 +322,37 @@ public void WorksWithStrings_MaintainsInsertionOrder()
 		Assert.AreEqual("alpha", set.ElementAt(1)); // Second unique
 		Assert.AreEqual("bravo", set.ElementAt(2)); // Third unique
 	}
+
+	[TestMethod]
+	public void Remove_WithCustomComparer_RemovesItemEqualOnlyUnderComparer()
+	{
+		// Arrange
+		InsertionOrderSet<string> set = new(StringComparer.OrdinalIgnoreCase) { "Apple", "Banana" };
+
+		// Act
+		bool removed = set.Remove("APPLE");
+
+		// Assert
+		Assert.IsTrue(removed);
+		Assert.HasCount(1, set);
+		Assert.IsFalse(set.Contains("apple"));
+		string[] expectedItems = ["Banana"];
+		Assert.AreSequenceEqual(expectedItems, set);
+	}
+
+	[TestMethod]
+	public void Remove_WithCustomComparer_ThenAdd_KeepsSingleElement()
+	{
+		// Arrange
+		InsertionOrderSet<string> set = new(StringComparer.OrdinalIgnoreCase) { "Apple" };
+
+		// Act
+		set.Remove("APPLE");
+		set.Add("apple");
+
+		// Assert
+		Assert.HasCount(1, set);
+		string[] expectedItems = ["apple"];
+		Assert.AreSequenceEqual(expectedItems, set);
+	}
 }

Containers/ContiguousSet.cs

@@ -281,8 +281,19 @@ public bool Remove(T item)
 			return false;
 		}
 
-		// Find and remove from the array
-		int index = Array.IndexOf(items, item, 0, Count);
+		// Find and remove from the array, matching with the set's comparer so an item that is
+		// equal only under a custom comparer is removed from storage as well as the hash set
+		IEqualityComparer<T> comparer = uniquenessSet.Comparer;
+		int index = -1;
+		for (int i = 0; i < Count; i++)
+		{
+			if (comparer.Equals(items[i], item))
+			{
+				index = i;
+				break;
+			}
+		}
+
 		if (index >= 0)
 		{
 			Count--;

Containers/InsertionOrderSet.cs

@@ -237,7 +237,15 @@ public bool Remove(T item)
 			return false;
 		}
 
-		items.Remove(item);
+		// Match with the set's comparer so an item that is equal only under a custom comparer
+		// is removed from the list as well as the hash set
+		IEqualityComparer<T> comparer = uniquenessSet.Comparer;
+		int index = items.FindIndex(x => comparer.Equals(x, item));
+		if (index >= 0)
+		{
+			items.RemoveAt(index);
+		}
+
 		return true;
 	}