uninserted key

malezjaa · malezjaa · commit 82a45ea9f1aa · 2026-04-16T21:17:57.000+02:00
diff --git a/src/rustc_entry.rs b/src/rustc_entry.rs
@@ -38,6 +38,7 @@ where
             RustcEntry::Occupied(RustcOccupiedEntry {
                 elem,
                 table: &mut self.table,
+                uninserted_key: Some(key)
             })
         } else {
             // Ideally we would put this in VacantEntry::insert, but Entry is not
@@ -85,6 +86,8 @@ pub struct RustcOccupiedEntry<'a, K, V, A = Global>
 where
     A: Allocator,
 {
+    /// Key that wasn't inserted because of an occupied entry.
+    uninserted_key: Option<K>,
     elem: Bucket<(K, V)>,
     table: &'a mut RawTable<(K, V), A>,
 }
@@ -304,6 +307,26 @@ impl<'a, K, V, A: Allocator> RustcOccupiedEntry<'a, K, V, A> {
         unsafe { &self.elem.as_ref().0 }
     }
 
+    /// Gets a reference to the key that wasn't inserted because of an occupied entry.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut map: HashMap<String, u32> = HashMap::new();
+    ///
+    /// // Pre-insert so we get an occupied entry
+    /// map.insert("poneyland".to_string(), 12);
+    ///
+    /// if let RustcEntry::Occupied(o) = map.rustc_entry("poneyland".to_string()) {
+    ///     let key = o.uninserted_key();
+    ///     println!("Got key back: {:?}", key);
+    /// }
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn uninserted_key(&mut self) -> &mut Option<K> {
+        &mut self.uninserted_key
+    }
+
     /// Take the ownership of the key and value from the map.
     ///
     /// # Examples
@@ -534,6 +557,7 @@ impl<'a, K, V, A: Allocator> RustcVacantEntry<'a, K, V, A> {
         RustcOccupiedEntry {
             elem: bucket,
             table: self.table,
+            uninserted_key: None
         }
     }
 }
