pub trait VacantEntry<'a> {
type K;
type V;
// Required methods
fn key(&self) -> &Self::K;
fn into_key(self) -> Self::K;
fn insert(self, v: Self::V) -> &'a mut Self::V;
}pub trait VacantEntry<'a> {
type K;
type V;
// Required methods
fn key(&self) -> &Self::K;
fn into_key(self) -> Self::K;
fn insert(self, v: Self::V) -> &'a mut Self::V;
}