A Rust version of Python's counter

counter.rs

use std::cmp::Eq;
use std::collections::HashMap;
use std::hash::Hash;

#[derive(Debug)]
struct Counter<V>
where
    V: Eq + Hash,
{
    map: HashMap<V, i32>,
}

impl<V> Counter<V>
where
    V: Eq + Hash,
{
    fn new<T: Iterator<Item = V>>(iter: T) -> Counter<V> {
        let mut hm = HashMap::new();
        for v in iter {
            let counter = hm.entry(v).or_insert(0);
            *counter += 1;
        }
        Counter { map: hm }
    }
}

impl<T: Hash + Eq> std::ops::Deref for Counter<T> {
    type Target = HashMap<T, i32>;
    fn deref(&self) -> &Self::Target {
        &self.map
    }
}

impl<T: Hash + Eq> std::iter::FromIterator<T> for Counter<T> {
    fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Self {
        Counter::new(iter.into_iter())
    }
}

fn main() {
    let c: Counter<_> = "hello world".chars().collect();
    println!("{:?}", Counter::new("hello world".chars()));
    println!(
        "{:?}",
        Counter::new(vec![1, 2, 3, 2, 2, 2, 5, 6, 7, 7, 8, 9, 10].iter())
    );
    for v in c.keys() {
        println!("{}", v);
    }
    println!("There are {} ls", c[&'l']);
}