Create immutable hash with data

• HashMap

• from

• keys

• We can also create a HashMap from existing data. In this case the hash does not have to be mutable.

use std::collections::HashMap;

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

    // counter.insert("other", 3); // cannot borrow `counter` as mutable, as it is not declared as mutable
}

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