Function cp_tricks::hashmap

pub fn hashmap()

Using entry in Hashmap for inplace manipulation

use std::collections::HashMap;
let mut letters = HashMap::new();
for ch in "a short treatise on fungi".chars() {
    let counter = letters.entry(ch).or_insert(0);
    *counter += 1;
}
assert_eq!(letters[&'s'], 2);
assert_eq!(letters[&'t'], 3);
assert_eq!(letters[&'u'], 1);
assert_eq!(letters.get(&'y'), None);