From 705442380446f6567124d9385dcd8d53c406f255 Mon Sep 17 00:00:00 2001
From: KaliCZ <kalandrapavel@gmail.com>
Date: Thu, 12 Oct 2023 15:20:30 +0200
Subject: [PATCH] Disallowed changing the items within NonEmptyEnumerable.

---
 .../Collections/NonEmptyEnumerable.cs         | 20 +++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/src/FuncSharp/Collections/NonEmptyEnumerable.cs b/src/FuncSharp/Collections/NonEmptyEnumerable.cs
index edf6b62..80544e5 100644
--- a/src/FuncSharp/Collections/NonEmptyEnumerable.cs
+++ b/src/FuncSharp/Collections/NonEmptyEnumerable.cs
@@ -76,11 +76,23 @@ private NonEmptyEnumerable(T head, IReadOnlyList<T> tail)
 
     public int Count { get; }
 
-    public T this[int index] => index switch
+    public T this[int index]
     {
-        0 => Head,
-        _ => Tail[index - 1]
-    };
+        get
+        {
+            if (index < 0 || index >= Count)
+            {
+                throw new ArgumentOutOfRangeException(nameof(index));
+            }
+
+            return index switch
+            {
+                0 => Head,
+                _ => Tail[index - 1]
+            };
+        }
+        set => throw new NotSupportedException("Cannot modify items within NonEmptyEnumerable.");
+    }
 
     public IEnumerator<T> GetEnumerator()
     {