From 22ab4de92ac855a02a2e8517148dfc69b2f3c49c Mon Sep 17 00:00:00 2001
From: Predrag Gruevski <obi1kenobi82@gmail.com>
Date: Mon, 6 Jul 2026 11:21:25 -0400
Subject: [PATCH] [perf] Add explicit `Iterator::count` impl for `ChunkBy`.

---
 library/core/src/slice/iter.rs | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/library/core/src/slice/iter.rs b/library/core/src/slice/iter.rs
index 18abdbed5af6f..6f75808015e71 100644
--- a/library/core/src/slice/iter.rs
+++ b/library/core/src/slice/iter.rs
@@ -3050,6 +3050,20 @@ where
         if self.slice.is_empty() { (0, Some(0)) } else { (1, Some(self.slice.len())) }
     }
 
+    #[inline]
+    fn count(mut self) -> usize {
+        let Some((mut previous, rest)) = self.slice.split_first() else {
+            return 0;
+        };
+
+        let mut count = 1;
+        for current in rest {
+            count += usize::from(!(self.predicate)(previous, current));
+            previous = current;
+        }
+        count
+    }
+
     #[inline]
     fn last(mut self) -> Option<Self::Item> {
         self.next_back()