I am not able to figure out why I am not getting keys filtered properly any hints

use std::collections::HashMap;

fn main() {
    let mut h: HashMap<&str, &str> = HashMap::new();
    h.insert("Hello", "World");
    h.insert("Aloha", "Wilkom");
    let dummy = h.keys().filter(|x| x.contains("Aloha"));
    println!("{:?}", dummy);
}

Output shows both the keys. I would expect only the key that matched

Filter { iter: ["Hello", "Aloha"] }

>Solution :

This is an artifact of the Debug impl for filter’s return value. If you collect the keys into a Vec it works as expected:

use std::collections::HashMap;

fn main() {
    let mut h:HashMap<&str,&str> = HashMap::new();
    h.insert("Hello","World");
    h.insert("Aloha","Wilkom");
    let dummy: Vec<_> = h.keys().filter(|x| x.contains("Aloha")).collect();
    println!("{:?}",dummy);
}

(playground)

If you directly print out Filter, you get:

Filter { iter: ["Aloha", "Hello"] }

which technically is correct: dummy is a filter based on the iterator ["Aloha", "Hello"]