Improved documentation for HashMap/BTreeMap Entry's .or_insert_with_key method

library/alloc/src/collections/btree/map/entry.rs

@@ -116,9 +116,12 @@ impl<'a, K: Ord, V> Entry<'a, K, V> {
         }
     }
 
-    /// Ensures a value is in the entry by inserting, if empty, the result of the default function,
+    /// Ensures a value is in the entry by inserting, if empty, the result of the default function.
-    /// which takes the key as its argument, and returns a mutable reference to the value in the
+    /// This method allows for generating key-derived values for insertion by providing the default
-    /// entry.
+    /// function a reference to the key that was moved during the `.entry(key)` method call.<br />
+    ///
+    /// The reference to the moved key is provided so that cloning or copying the key is
+    /// unnecessary, unlike with `.or_insert_with(|| ... )`.
     ///
     /// # Examples
     ///

library/std/src/collections/hash/map.rs

@@ -2222,9 +2222,12 @@ impl<'a, K, V> Entry<'a, K, V> {
         }
     }
 
-    /// Ensures a value is in the entry by inserting, if empty, the result of the default function,
+    /// Ensures a value is in the entry by inserting, if empty, the result of the default function.
-    /// which takes the key as its argument, and returns a mutable reference to the value in the
+    /// This method allows for generating key-derived values for insertion by providing the default
-    /// entry.
+    /// function a reference to the key that was moved during the `.entry(key)` method call.
+    ///
+    /// The reference to the moved key is provided so that cloning or copying the key is
+    /// unnecessary, unlike with `.or_insert_with(|| ... )`.
     ///
     /// # Examples
     ///