map Add in Rust 1.55

In Rust, the HashMap collection is used to represent a hash (also known as a dictionary or map) of key-value pairs. To add an element to a hash, you can use the insert() method of the HashMap. Here's an example:

use std::collections::HashMap;
fn main() {

    let mut hash_map = HashMap::new();
// Add a key-value pair to the hash map

    hash_map.insert("apple", 3);
// Print the hash map

    println!("{:?}", hash_map);

}

In this example, we first create a new, empty hash map using the HashMap::new() function. We then use the insert() method of this hash map to add a new key-value pair with the key "apple" and the value 3. Finally, we print out the entire hash map using the {:?} format specifier.

You can also add multiple key-value pairs to a hash in a single insert() call by passing in a tuple of key-value pairs. Here's an example:

use std::collections::HashMap;
fn main() {

    let mut hash_map = HashMap::new();
// Add multiple key-value pairs to the hash map

    hash_map.insert("apple", 3);

    hash_map.insert("banana", 2);

    hash_map.insert("orange", 5);
// Print the hash map

    println!("{:?}", hash_map);

}

In this case, we again use the HashMap::new() function to create a new hash map, but we add three key-value pairs to it in a single insert() call. This time, we print out the entire hash map using the {:?} format specifier as before.

Note that when you add a new key-value pair to a hash in Rust using the insert() method, if the key already exists in the hash, its previous value will be replaced with the new value.