Iterate over keys of a hash

---

examples/hashes/iterate-over-keys/src/main.rs

use std::collections::HashMap;

fn main() {
    let counter = HashMap::from([
        ("foo", 1),
        ("bar", 2),
    ]);
    println!("{:?}", counter);
    println!("{:?}", counter.keys());

    for name in counter.keys() {
        println!("{} : {}", name, counter[name]);
    }
}

{"bar": 2, "foo": 1}
["bar", "foo"]
bar : 2
foo : 1