pub fn vacant_ref(&self) -> &VacantEntry {
        use self::Entry::*;

        match self {
            Vacant(entry) => entry,
            Occupied(_) => panic!("expected vacant entry"),
        }
    }
/// Returns an immutable reference to the vacant entry.
///
/// # Panics
///
/// Panics if the variant is actually [`Entry::Occupied`].
Returns an immutable reference to the vacant entry.
Returns an immutable reference to the vacant entry .
pub fn vacant_ref(&self) -> &VacantEntry {
        use self::Entry::*;
        match self {
            Vacant(entry) => entry,
            Occupied(_) => panic!("expected vacant entry"),
        }
    }
pub fn vacant_ref ( & self ) -> & VacantEntry { use self :: Entry :: * ; match self { Vacant ( entry ) => entry , Occupied ( _ ) => panic ! ( " " ) , } }
Returns an immutable reference to the vacant entry.
Returns an immutable reference to the vacant entry .
&self
&self
panics
Panics if the variant is actually [`Entry::Occupied`].
Panics if the variant is actually [ ` Entry :: Occupied ` ] .