Update map.rs

Removing unnecessary additional third copy operation

Author: JustForFun88

src/map.rs

@@ -3587,10 +3587,8 @@ impl<'a, K, V, S, A: Allocator + Clone> OccupiedEntry<'a, K, V, S, A> {
     /// assert_eq!(map["poneyland"], 15);
     /// ```
     #[cfg_attr(feature = "inline-more", inline)]
-    pub fn insert(&mut self, mut value: V) -> V {
-        let old_value = self.get_mut();
-        mem::swap(&mut value, old_value);
-        value
+    pub fn insert(&mut self, value: V) -> V {
+        mem::replace(self.get_mut(), value)
     }
 
     /// Takes the value out of the entry, and returns it.
@@ -4256,10 +4254,8 @@ impl<'a, 'b, K, Q: ?Sized, V, S, A: Allocator + Clone> OccupiedEntryRef<'a, 'b,
     /// assert_eq!(map["poneyland"], 15);
     /// ```
     #[cfg_attr(feature = "inline-more", inline)]
-    pub fn insert(&mut self, mut value: V) -> V {
-        let old_value = self.get_mut();
-        mem::swap(&mut value, old_value);
-        value
+    pub fn insert(&mut self, value: V) -> V {
+        mem::replace(self.get_mut(), value)
     }
 
     /// Takes the value out of the entry, and returns it.