From d86e6d26c091b22e0ea544904771959c31433258 Mon Sep 17 00:00:00 2001
From: Mikolaj Wielgus <wielgusmikolaj@gmail.com>
Date: Sat, 26 Sep 2026 02:27:19 +0200
Subject: [PATCH] Implement `Index` and `IndexMut` traits

It's useful to have `Index` and `IndexMut` traits implemented if you
want to have code that is generic over indexable containers, like this:

```
fn increment<C>(container: &mut C, index: usize)
where
    C: std::ops::IndexMut<usize>,
    C::Output: std::ops::AddAssign<i32>,
{
    container[index] += 1;
}
```

Having these traits is also consistent with `Vec`, which also implements
them.

I have added two tests to test these traits.
---
 src/references.rs | 23 +++++++++++++++++++++--
 tests/main.rs     | 13 +++++++++++++
 2 files changed, 34 insertions(+), 2 deletions(-)

diff --git a/src/references.rs b/src/references.rs
index 0582ea12..06b4a381 100644
--- a/src/references.rs
+++ b/src/references.rs
@@ -10,8 +10,11 @@ use {
         },
         ops::{
             Deref,
-            DerefMut
-        }
+            DerefMut,
+            Index,
+            IndexMut
+        },
+        slice::SliceIndex
     }
 };
 
@@ -55,3 +58,19 @@ impl<T, const N: usize, A: Allocator> DerefMut for SmallVec<T, N, A> {
         self.as_mut_slice()
     }
 }
+
+impl<T, const N: usize, A: Allocator, I: SliceIndex<[T]>> Index<I> for SmallVec<T, N, A> {
+    type Output = <I as SliceIndex<[T]>>::Output;
+
+    #[inline]
+    fn index(&self, index: I) -> &Self::Output {
+        &self.deref()[index]
+    }
+}
+
+impl<T, const N: usize, A: Allocator, I: SliceIndex<[T]>> IndexMut<I> for SmallVec<T, N, A> {
+    #[inline]
+    fn index_mut(&mut self, index: I) -> &mut Self::Output {
+        &mut self.deref_mut()[index]
+    }
+}
diff --git a/tests/main.rs b/tests/main.rs
index 0c230d87..d58fcc02 100644
--- a/tests/main.rs
+++ b/tests/main.rs
@@ -629,6 +629,19 @@ fn borrow_mut() {
     assert_eq!(a.borrow_mut(), [1, 4, 3]);
 }
 
+#[test]
+fn index() {
+    let a = SmallVec::<u32, 2>::from(&[1, 2, 3][..]);
+    assert_eq!(a[1], 2);
+}
+
+#[test]
+fn index_mut() {
+    let mut a = SmallVec::<u32, 2>::from(&[1, 2, 3][..]);
+    a[1] = 22;
+    assert_eq!(a[1], 22);
+}
+
 #[test]
 fn from() {
     assert_eq!(&SmallVec::<u32, 2>::from(&[1][..])[..], [1]);