Create immutable hash with data

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

examples/hashes/create-hash-with-data/src/main.rs

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"]