gistfile1.txt

trait ExtendValues<T> {
    fn extend_values<I>(&mut self, iter: I)
    where
        I: Iterator<Item = T>;
}

impl<K, V, E, T> ExtendValues<(K, E)> for HashMap<K, V>
where
    K: Eq + std::hash::Hash,
    V: Default + Extend<T>,
    E: IntoIterator<Item = T>,
{
    fn extend_values<I>(&mut self, iter: I)
    where
        I: IntoIterator<Item = (K, E)>,
    {
        for (k, e) in iter {
            self.entry(k).or_default().extend(e);
        }
    }
}