Method count

src/plan/hector.rs:1032–1044

(
        &mut self,
        prefixes: &Collection<S, (P, usize, usize)>,
        index: usize,
    )

    type Extension = V;

    fn count(
        &mut self,
        prefixes: &Collection<S, (P, usize, usize)>,
        index: usize,
    ) -> Option<Collection<S, (P, usize, usize)>> {
        Some(prefixes.map(move |(prefix, old_count, old_index)| {
            if 1 < old_count {
                (prefix.clone(), 1, index)
            } else {
                (prefix.clone(), old_count, old_index)
            }
        }))
    }

    fn propose(&mut self, prefixes: &Collection<S, P>) -> Collection<S, (P, V)> {
        let value = self.value.clone();