Merge HashMaps (extend)

---

• If the same key appears twice, the value of the second one wins.

examples/hashes/merge/src/main.rs

use std::collections::HashMap;
fn main() {
    let a = HashMap::from([("apple", 1), ("banana", 1)]);
    let b = HashMap::from([("apple", 2), ("peach", 2), ("grape", 2)]);

    let mut total: HashMap<&str, i32> = HashMap::new();
    total.extend(a);
    println!("{:#?}", total);

    total.extend(b);
    println!("{:#?}", total);
}

{
    "apple": 1,
    "banana": 1,
}
{
    "peach": 2,
    "banana": 1,
    "grape": 2,
    "apple": 2,
}