pub fn front_mut(&mut self) -> Option<&mut EntryData> {
        let index = self.head()?;

        match &mut self.entries[index] {
            Entry::Occupied(entry) => Some(&mut entry.value),
            _ => None,
        }
    }
/// Returns a mutable reference to the value at the front of the list, if it exists.
///
/// Complexity: O(1)
///
/// # Examples
///
/// ```
/// use dlv_list::VecList;
///
/// let mut list = VecList::new();
/// assert_eq!(list.front_mut(), None);
///
/// list.push_front(0);
/// list.push_front(5);
///
/// let mut front = list.front_mut().unwrap();
/// assert_eq!(front, &mut 5);
/// *front *= 2;
///
/// assert_eq!(list.front(), Some(&10));
/// ```
Returns a mutable reference to the value at the front of the list, if it exists.
Returns a mutable reference to the value at the front of the list if it exists .
pub fn front_mut(&mut self) -> Option<&mut EntryData> {
        let index = self.head()?;
        match &mut self.entries[index] {
            Entry::Occupied(entry) => Some(&mut entry.value),
            _ => None,
        }
    }
pub fn front_mut ( & mut self ) -> Option < & mut EntryData > { let index = self . head ( ) ? ; match & mut self . entries [ index ] { Entry :: Occupied ( entry ) => Some ( & mut entry . value ) , _ => None , } }
Returns a mutable reference to the value at the front of the list, if it exists.
Returns a mutable reference to the value at the front of the list if it exists .
&mut self
&mut self
examples
```
use dlv_list::VecList.

let mut list = VecList::new();
assert_eq!(list.front_mut(), None).

list.push_front(0);
list.push_front(5).

let mut front = list.front_mut().unwrap();
assert_eq!(front, &mut 5);
front *= 2.


` ` ` use dlv_list :: VecList . let mut list = VecList :: new () ; assert_eq! ( list . front_mut () None ) . list . push_front ( 0 ) ; list . push_front ( 5 ) . let mut front = list . front_mut () . unwrap () ; assert_eq! ( front &mut 5 ) ; front * = 2 .