From 1120cb2fe54fae7a1a8ccd5beb941f5b207084c0 Mon Sep 17 00:00:00 2001
From: Cameron Steffen <cam.steffen94@gmail.com>
Date: Tue, 15 Jul 2025 14:14:22 -0500
Subject: [PATCH] Add LocalKey<Cell>::update

---
 library/std/src/thread/local.rs | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/library/std/src/thread/local.rs b/library/std/src/thread/local.rs
index 7cd448733130d..0ad014ccd3e2e 100644
--- a/library/std/src/thread/local.rs
+++ b/library/std/src/thread/local.rs
@@ -469,6 +469,29 @@ impl<T: 'static> LocalKey<Cell<T>> {
     pub fn replace(&'static self, value: T) -> T {
         self.with(|cell| cell.replace(value))
     }
+
+    /// Updates the contained value using a function.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(local_key_cell_update)]
+    /// use std::cell::Cell;
+    ///
+    /// thread_local! {
+    ///     static X: Cell<i32> = const { Cell::new(5) };
+    /// }
+    ///
+    /// X.update(|x| x + 1);
+    /// assert_eq!(X.get(), 6);
+    /// ```
+    #[unstable(feature = "local_key_cell_update", issue = "143989")]
+    pub fn update(&'static self, f: impl FnOnce(T) -> T)
+    where
+        T: Copy,
+    {
+        self.with(|cell| cell.update(f))
+    }
 }
 
 impl<T: 'static> LocalKey<RefCell<T>> {