[Rust] map demo

// Call HashMap class in Rust standard library
use std::collections::HashMap;

fn main() {
    // Create an empty map
    let mut hash = HashMap::new();  // HashMap<&str, &str>

    // Insert (key, value) pairs into the map
    hash.insert("one", "eins");
    hash.insert("two", "zwei");
    hash.insert("three", "drei");

    // Get value by key
    assert_eq!(hash.get("one"), Some(&"eins"));

    // Get None when (key, value) doesn't exist
    assert_eq!(hash.get("four"), None);
}