Add OccupiedEntry::shift_remove() and swap_remove()

Author: GREsau

src/map.rs

@@ -876,6 +876,12 @@ impl<'a> OccupiedEntry<'a> {
 
     /// Takes the value of the entry out of the map, and returns it.
     ///
+    /// If serde_json's "preserve_order" is enabled, `.remove()` is
+    /// equivalent to [`.swap_remove()`][Self::swap_remove], replacing this
+    /// entry's position with the last element. If you need to preserve the
+    /// relative order of the keys in the map, use
+    /// [`.shift_remove()`][Self::shift_remove] instead.
+    ///
     /// # Examples
     ///
     /// ```
@@ -896,11 +902,39 @@ impl<'a> OccupiedEntry<'a> {
     #[inline]
     pub fn remove(self) -> Value {
         #[cfg(feature = "preserve_order")]
-        return self.occupied.swap_remove();
+        return self.swap_remove();
         #[cfg(not(feature = "preserve_order"))]
         return self.occupied.remove();
     }
 
+    /// Takes the value of the entry out of the map, and returns it.
+    ///
+    /// Like [`Vec::remove`], the entry is removed by shifting all of the
+    /// elements that follow it, preserving their relative order. This perturbs
+    /// the index of all of those elements!
+    ///
+    /// [`Vec::remove`]: std::vec::Vec::remove
+    #[cfg(feature = "preserve_order")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "preserve_order")))]
+    #[inline]
+    pub fn shift_remove(self) -> Value {
+        self.occupied.shift_remove()
+    }
+
+    /// Takes the value of the entry out of the map, and returns it.
+    ///
+    /// Like [`Vec::swap_remove`], the entry is removed by swapping it with the
+    /// last element of the map and popping it off. This perturbs the position
+    /// of what used to be the last element!
+    ///
+    /// [`Vec::swap_remove`]: std::vec::Vec::swap_remove
+    #[cfg(feature = "preserve_order")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "preserve_order")))]
+    #[inline]
+    pub fn swap_remove(self) -> Value {
+        self.occupied.swap_remove()
+    }
+
     /// Removes the entry from the map, returning the stored key and value.
     ///
     /// If serde_json's "preserve_order" is enabled, `.remove_entry()` is