From f4cdcad75e339106d866cf0ce9298faab36a3205 Mon Sep 17 00:00:00 2001
From: Klim Tsoutsman <klim@tsoutsman.com>
Date: Wed, 17 Jun 2026 10:10:59 +0200
Subject: [PATCH] Add `map` to `SlotMap`

Similar to #133, but now the `map` function takes `self` i.e.

```
pub fn map<U, F>(self, mut f: F) -> SlotMap<K, U>
where
        F: FnMut(K, V) -> U
```

Signed-off-by: Klim Tsoutsman <klim@tsoutsman.com>
---
 src/basic.rs | 60 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 60 insertions(+)

diff --git a/src/basic.rs b/src/basic.rs
index 81f77e6..f13a9ac 100644
--- a/src/basic.rs
+++ b/src/basic.rs
@@ -64,6 +64,34 @@ impl<T> Slot<T> {
             }
         }
     }
+
+    fn map<K, U, F>(self, key_idx: u32, mut f: F) -> Slot<U>
+    where
+        K: Key,
+        F: FnMut(K, T) -> U,
+    {
+        let mut this = ManuallyDrop::new(self);
+        let version = this.version;
+
+        if this.occupied() {
+            let key = KeyData::new(key_idx, version).into();
+            let value = unsafe { ManuallyDrop::take(&mut this.u.value) };
+
+            Slot {
+                u: SlotUnion {
+                    value: ManuallyDrop::new(f(key, value)),
+                },
+                version,
+            }
+        } else {
+            let next_free = unsafe { this.u.next_free };
+
+            Slot {
+                u: SlotUnion { next_free },
+                version,
+            }
+        }
+    }
 }
 
 impl<T> Drop for Slot<T> {
@@ -1006,6 +1034,38 @@ impl<K: Key, V> SlotMap<K, V> {
             inner: self.iter_mut(),
         }
     }
+
+    /// Returns a new slotmap preserving the keys, but mapping the values with `f`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use slotmap::*;
+    /// let mut sm = SlotMap::new();
+    /// let k1 = sm.insert(1);
+    /// let k2 = sm.insert(2);
+    ///
+    /// let sm = sm.map(|_k, v| v.to_string());
+    /// assert_eq!(sm[k1], "1");
+    /// assert_eq!(sm[k2], "2");
+    /// ```
+    pub fn map<U, F>(self, mut f: F) -> SlotMap<K, U>
+    where
+        F: FnMut(K, V) -> U,
+    {
+        let mut new_slots = Vec::with_capacity(self.slots.capacity());
+
+        for (idx, slot) in self.slots.into_iter().enumerate() {
+            new_slots.push(slot.map(idx as u32, &mut f));
+        }
+
+        SlotMap {
+            slots: new_slots,
+            free_head: self.free_head,
+            num_elems: self.num_elems,
+            _k: PhantomData,
+        }
+    }
 }
 
 impl<K: Key, V> Clone for SlotMap<K, V>